(A structure with a pair of steel doors sits incongruously in the steaming alien jungle on the reddish brown planet. A slim human with a white beard comes out and plants a sign at the head of a mound off to the left of the structure. The sign reads - Egard Lumb died here 7y2 in the year 37,166. It is not the only grave marker we can see.)

[Mine]

(A young man collects crystals and puts them into a machine which pulverises them. He passes the remains over to another man then goes to answer the radio.)
BALDWIN: Yep?

[Expedition base]

BRAUN: Base checking. You all right out there?
BALDWIN [OC]: All quiet.

[Mine]

BRAUN [OC]: Where are you?
BALDWIN: Sector five. We've hit a rich load.

[Expedition base]

BRAUN: Sector five? Listen, I just took a sun shot. You have fifteen degrees to full night. You'd better get out of there fast.

[Mine]

BALDWIN: Right. Professor, that was Braun. We've got to leave.
SORENSON: What?
BALDWIN: It's fifteen degrees to night.
SORENSON: Just look at this, Baldwin. It's showing more than seventy pure.
BALDWIN: We'll never make base from here, sir, if we don't leave now.
SORENSON: The last time we hit a vein as rich as this, you know what happened?
BALDWIN: Yes. Lorenzo died. He was the first. That's when it all seemed to start.
SORENSON: We lost it. The vein vanished. This damned planet took it back. It's alive, you know, Baldwin. It watches every move we make. I won't be beaten again. Load the canisters.
BALDWIN: Professor, please. There isn't time now. We can return tomorrow.
SORENSON: It'll be gone by tomorrow. Don't you see, man? It knows. It senses what we're trying to do.
BALDWIN: I'm not trekking back through that jungle in the dark. If you don't come now, I shall have to leave you.
SORENSON: Well, then, leave. Leave.
(Back at base, Braun checks his chronometer, takes a rifle from the wall and goes outside. Something crackles in the jungle nearby. Braun backs away, frightened, then falls. He appears to be trying to push away something heavy but invisible, then he vanishes. The crackling fades away.)

[Outside Expedition base]

(Baldwin splashes his way through a swampy section of jungle in the dark and makes it safely back to Base.)
BALDWIN: Braun? Braun?

[Expedition base]

BALDWIN: Sorenson wouldn't come. He. Braun? Where are you?
(The crackling sound starts up. Baldwin manages to press a panic button before it pushes him into a rear compartment and down onto the floor. Still struggling, Baldwin fades away.)

[Tardis]

(The Doctor is working the console while Sarah checks her watch.)
SARAH: How long have we been travelling?
DOCTOR: Hmm? What did you say?
SARAH: You promised me we'd be back in London five minutes before leaving Loch Ness.
DOCTOR: Did I?
SARAH: Oh, you're trying to wriggle out of it.
DOCTOR: Wriggle out of what?
SARAH: Your promise.
DOCTOR: Listen, we're on the edge of a time-space vortex and you're talking in minutes.
SARAH: Oh, I see. What's gone wrong this time?
DOCTOR: Nothing. Nothing at all. What makes you think something's gone wrong?
SARAH: Because you always get rude when you're trying to cover up a mistake.
DOCTOR: Nothing of consequence. Slight overshoot, easily rectified.
SARAH: Come on, where are we?
DOCTOR: We've come out of the time vortex at the wrong point, that's all. A few years too late.
SARAH: How many?
DOCTOR: Thirty thousand.
(A beeping sound starts up.)
SARAH: That's a distress call.
DOCTOR: Someone's in trouble.
SARAH: Where?
DOCTOR: Who knows? Stand by for emergency materialisation.

[Jungle]

(The Tardis materialises and the Doctor looks out, then steps out holding his direction finder. Sarah follows.)
SARAH: Which way?
DOCTOR: This way.
(A little further on.)
SARAH: You don't know where we are.
DOCTOR: Oh, with any luck, we're near enough to reach wherever it is.
SARAH: That is not what I meant.
DOCTOR: Before whatever it was that made them transmit the call overwhelms them. That is, if we're not too late already.
SARAH: I mean, what planet?
DOCTOR: Oh, it's a weak signal. Allowing for the fact of interference from the time warp, could you move any faster?
SARAH: I'm doing the best I can.
(The crackling starts up and Sarah becomes rigid, her fingers stretched out.)

[Space probe command area]

(A craft approaches the planet.)
VISHINSKY: There it is, Zeta Minor. The last planet of the known universe.
(He walks up steps at the back of the bridge to where Prentis Hancock sits at a glass table.)
SALAMAR: Crew deck, orbital entry imminent. Ponti and de Haan to command area. Ponti and de Haan to command area. Vishinsky, you'll lead the landing party.
VISHINSKY: Without Ponti?
SALAMAR: You are the most experienced officer.
VISHINSKY: You are going to scan first?
SALAMAR: No.
VISHINSKY: It's advised procedure before physical landing on any ex-planet.
SALAMAR: Technically, Zeta Minor is not an ex-planet. Professor Sorenson's party's been on the surface for months.
VISHINSKY: They might have been dead for months. They've not reported.
SALAMAR: Vishinsky, you know our fuel position. We've enough for the return journey and an emergency reserve. I cannot waste that on a low level scan.
VISHINSKY: It's your decision, Controller. I'll get equipped for descent.

[Jungle]

(The Doctor notices Sarah is not moving. The crackling has stopped.)
DOCTOR: Sarah? You all right? What's the matter?
SARAH: I don't know. Just suddenly felt so odd, as though my mind left my body.
DOCTOR: Are you all right now?
SARAH: Yes.
DOCTOR: You look all right.
SARAH: Yeah. What's that you've found?
DOCTOR: Hand tool of some kind.
(Like a pick axe, but all metal.)
SARAH: So the people who sent that signal must be humanoid. Well, if they've got hands?

[Space probe command area]

(Two armed men enter the control area and the Controller goes down to speak to them.)
SALAMAR: The descent chamber's ready, Ponti.
PONTI: (Jamaican) Yes, Controller.
SALAMAR: The probe will remain in free orbit in case emergency escape procedures are needed. From the time you land, maintain permanent audio contact.
DE HAAN: Understood, Controller.
SALAMAR: The descent area is the one selected for Sorenson, so you should have no difficulty locating the base.
VISHINSKY: Unless something gets in our way.
SALAMAR: You're equipped and trained to deal with all normal contingencies. The prime purpose of this mission is to locate Professor Sorenson's expedition. If hostile forces are found to be operating on Zeta Minor, we've the capacity to eliminate them.
(An alarm sounds.)
SALAMAR: Right, we're in orbit. Prepare for descent.
(Vishinsky, Ponti and de Haan enter Compression Area Z2.)

[Outside the Expedition base]

(The Doctor and Sarah arrive at the graveyard and find a desiccated corpse on the ground.)
SARAH: Looks like we're too late.
DOCTOR: Several months too late, by the look of him.

[Expedition base]

(It is dark inside.)
DOCTOR: Anyone about? No one about.
SARAH: Can't we have some lights?
DOCTOR: Probably the power's run down.
SARAH: That would account for the weak signal.
DOCTOR: Yes. Ah.
SARAH: What?
DOCTOR: Automatic distress button. It all adds up. May have been running for months. High capacity power cell dependant for sunlight on charging.
SARAH: So we're still in the solar system.
DOCTOR: We're still in a solar system, but what particular star provides the light and energy? Wherever we are, we're a long way out. SARAH: I wonder what happened here?
DOCTOR: Hmm? Well, this is clearly the base for some kind of scientific expedition, possibly geological. Something went wrong and they sent out a distress signal.
SARAH: And died before help arrived.
DOCTOR: Yes, something like that. A lost expedition.
SARAH: So, what are we going to do?
DOCTOR: So, let's go back to the Tardis and fetch my spectromixer, and I'll fix our position by that star. Then I'll repair this power cell and try and make contact.
SARAH: Well, you can get on with that now. I'll fetch the spectromixer.
DOCTOR: Good idea. Would you do that?
SARAH: Why not? I know the way.
DOCTOR: Good thinking. What are you waiting for?
SARAH: The key.
DOCTOR: Oh.
(The Doctor gives Sarah the Tardis key.)
SARAH: Right. See you.
(Sarah leaves. A mechanical whirring sound comes from the rear compartment. The Doctor opens the door and enters. He finds Baldwin's desiccated remains on the floor.)
DOCTOR: Sarah.

[Outside the Tardis]

(Sarah has made it back to the Tardis. Something parts a bush with invisible hands and watches her go inside. Then de Haan, Ponti, Vishinsky and two other men arrive.)
VISHINSKY: Don't touch. Keep back. It may be a trap. Landing party to probe.
(Inside the Tardis, Sarah is rummaging through a Gladstone bag.)

[Space probe command area]

SALAMAR: Understood. You've acted correctly. Do not attempt entry.
VISHINSKY [OC]: Shall we apply disintegrators?
SALAMAR: On no account. It'll yield essential information on hostile forces. Your orders are, transpose object to probe. Out. Prepare the quarantine berth.

[Outside the Tardis]

(The landing party attach devices to the outside of the Tardis as someone watches from the bushes. Inside, Sarah finds the device she needs and puts it in her jeans pocket, then goes to open the doors. They do not move. She tries again then goes over to pull at them herself.)
VISHINSKY: All right, stand clear.
(The Tardis vanishes.)
VISHINSKY: Movement. Over there. Approach and identify yourself.
(A man comes up to them.)
VISHINSKY: Professor Sorenson!
SORENSON: I've been observing you for some time. One has to be careful on this planet. Appearances can be deceptive.
VISHINSKY: You all right, Professor?
SORENSON: Oh, yes. It's nearly dawn. The days are quite safe.
VISHINSKY: But how are you? Galactic Mission Control received no word from you. They sent us to investigate.
SORENSON: I'm well. I'm more than well. My theory about Zeta Minor has proved to be true. Only last night I made the vital discovery in Sector five.
VISHINSKY: Where are the others?
SORENSON: Baldwin returned to the base last night. He was suffering from, from fatigue. He'll be fine now. Come, I'll show you the way.
VISHINSKY: There were eight in your expedition.
SORENSON: Yes, we've had difficulties. Conditions are hard. We've lost some, but the important thing is the mission has been a success. We found what we came to find.
VISHINSKY: How many have you lost?
SORENSON: He'll be fine now. It's just tiredness. He needs a good rest. It's not far.

[Base rear compartment]

(The Doctor looks up to see a trio of weapons pointed at him through the doorway. Sorenson pushes past and sees the corpse on the floor.)
SORENSON: Baldwin?
DOCTOR: He's dead.
SORENSON: Yes. Murdered. Just like the others.
VISHINSKY: Stay where you are.

[Quarantine berth]

(Sarah tries the door controls again and this time they open. She picks up the metal hand axe the Doctor had found and goes outside. Salamar and a guard stand in an observation balcony area.)
SALAMAR: Stand just where you are.
SARAH: Where am I?
SALAMAR: You are in orbit around planet Zeta Minor. You're a Morestran prisoner.
SARAH: I can't breathe.
SALAMAR: An oxygen type. Could be an Earthling. Transfer oxygen to quarantine area.
MORELLI: Command deck calling you, Commander.
(Say hi to Michael Wisher, free from the Davros makeup.)
SALAMAR: Right. Complete the quarantine procedures and bring the alien to me. You see what she's holding?

[Expedition base]

(The hand axe is missing from a rack of tools on the wall. Vishinsky is reporting in.)
VISHINSKY: He calls himself the Doctor. He's not of our world. Claims to have landed in response to a distress call.

[Space probe command area]

SALAMAR: Have you checked the transmitters down there?

[Expedition base]

VISHINSKY: Yes, but any signal would have been monitored by our receivers.
DOCTOR: Perhaps my receivers are better than yours.
PONTI: Shut up!
DOCTOR: My manners certainly are.

[Space probe command area]

SALAMAR: Can't Sorenson explain?
VISHINSKY [OC]: He's too shocked. His mental state is strained.
(Sarah is brought in.)
SALAMAR: Understandable. We arrived just in time. And the prisoner?
VISHINSKY [OC]: Just repeats the same story.
SALAMAR: Keep a careful watch on him. I may have better fortune.
(Down on the planet, something roars and crackles through the jungle.)
SALAMAR: You picked it up?
SARAH: That's what I said. We picked up a distress call and landed immediately.
SALAMAR: Do you have any idea where Zeta Minor is situated?
SARAH: No, not exactly.
SALAMAR: It's beyond Cygnus A. It's as distant again from Ortoro galaxy as that galaxy is from the Anterades. It's on the very edge of the known universe. You just happened to be passing when you received this distress call?
SARAH: Well, no, no, no, we were on our way to London, to Earth.
SALAMAR: To Earth? You said you came from Earth.
SARAH: Yes, we do. That is, I do. You see, the Doctor said we could, we could be back
(The comm. beeps and Salamar answers it.)
SALAMAR: Report.
MORELLI [OC]: Landing site moving to obverse. Decision to land on planet or continue in orbit imperative.
SALAMAR: We'll go in now, before night. I think you and your friend, the Doctor, know much more about Zeta Minor than you want us to think. Take her away. Commence landing procedure.

[Expedition base]

(Armed men leave the spacecraft, which has quietly touched down next to the graveyard, and gather round the door to the Base. Salamar listens to Sorenson's story.)
SORENSON: We'd only been working a few weeks when Lorenzo went. After that, Gura and then Summers. And then for a while, it stopped. We thought that we were safe, that whatever it was had decided to leave us in peace, but it wasn't to be.
VISHINSKY: The killings always happened at night?
SORENSON: Oh, yes. The nights are the worst.
SALAMAR: Naturally. Any force of alien infiltrators is going to operate under cover of dark. A full and immediate confession would save you great discomfort.
DOCTOR: Discomfort? You mean you're going to torture me.
SALAMAR: Interrogate you. And nobody, Doctor, withstands Morestran interrogation for very long. Put him with the other prisoner.
(The Doctor is taken away.)
SALAMAR: We must try and contact the home planet again.
VISHINSKY: Not a chance, Controller. This far our, we're on our own.
(Ponti and de Haan enter.)
SALAMAR: Well?
PONTI: We've searched a wide belt of the jungle in all directions. No sign of any other life.
SALAMAR: So that seems to narrow the killer down to our two aliens. Prepare to execute them.

[Base crew quarters]

SARAH: Let's go, shall we?
DOCTOR: How?
SARAH: Through the window.
DOCTOR: They're magnetically locked.
SARAH: But the power is low.
(The Doctor goes to the window and starts to push the pane downwards.)

[Outside the Expedition base]

(A sentry walks by as the crackling starts up. The Doctor and Sarah appear from the side of the building to see a large energy creature straight out of Forbidden Planet. They try to retreat but Sarah falls, and the entity looms over them.)

Part Two

[Outside the Expedition base]

(The sentry returns and fires at the energy creature, allowing the Doctor and Sarah to get away. The creature smothers him, and he and his weapon fade away. Ponti and de Haan arrive as the creature leaves.)
PONTI: Nothing.
DE HAAN: I heard a scream.
PONTI: Who's the guard on this sector?
DE HAAN: O'Hara. There's no sign of him.
PONTI: Let's get some lights round here.
DE HAAN: Right. I'll go and look for him.
(Ponti and de Haan leave, then O'Hara's desiccated remains pop back into view.)
DOCTOR: All right, Sarah, I think it's gone. Are you all right? What's the matter?
SARAH: It's how I felt before, in the jungle. As though I was being drawn from my body.
DOCTOR: You've had a very narrow escape.
(They go over to O'Hara's body.)
SARAH: What was it?
DOCTOR: I'm not sure yet, but I've got a very unpleasant theory.

[Expedition base]

SALAMAR: Everything's normal now.
VISHINSKY: Something caused that power drain. There was a temperature drop of four degrees.
PONTI: Controller!
VISHINSKY: Later, Ponti. We have a systems fault.
PONTI: I think the base is under attack, Controller.
SALAMAR: Under attack?
PONTI: We've heard something out there. And O'Hara seems to have disappeared. We need lights.
SALAMAR: Better check the prisoners, Vishinsky.

[Base crew quarters]

SALAMAR: As I thought.
VISHINSKY: I'll call the crew to alert.

[Outside the Expedition base]

SARAH: It's as if life was sucked out of him.
(An alarm sounds.)
DOCTOR: Come on. I think we've been missed.

[Jungle]

PONTI: Halt!
(The guards fire at the fleeing figures, and miss.)

[Expedition base]

VISHINSKY: With the power drain, the magnetic lock must have failed.
SALAMAR: Obviously. But we still don't know what caused it.
(Ponti enters.)
SALAMAR: What is it?
PONTI: Something you should see for yourself, Controller. They've killed O'Hara.

[Outside the Expedition base]

SALAMAR: They must be recaptured and made to pay for this.
PONTI: We won't find them in this jungle.
SALAMAR: They won't escape. We'll launch the oculoid tracker at first light.
PONTI: Very good, Controller.
SALAMAR: Get Sorenson. I want him to see this.
VISHINSKY: He's under medicare in the probe.
SALAMAR: Bring him here immediately, Vishinsky. And I want a full bio-analysis on the cause of death.
VISHINSKY: All right.

[Jungle]

SARAH: It's so dark.
DOCTOR: Just hang on.
SARAH: What's the matter?
DOCTOR: Nothing.
SARAH: Where are we going?
DOCTOR: Shush. Listen. It's coming this way.
(Lianas and seed pods sway as the crackling passes by.)
SARAH: (sotto) That was lucky.
DOCTOR: Fortunately, time is on our side.
SARAH: Time?
DOCTOR: Yes. Night's candles are burned out and jocund day stands tiptoe on the misty mountain top. Or something like that.
(Close - it is burnt out. Romeo + Juliet Act 3 Scene 5.)
SARAH: Ah, you mean it's getting light.
DOCTOR: That's what Shakespeare meant.
SARAH: Doesn't it like daylight?
DOCTOR: That is the question.
SARAH: Oh, Doctor, where are you going?

[Space probe command area]

VISHINSKY: Projectile chamber three, ignition procedures activate.
MORELLI [OC]: Projectile chamber three activated. Oculoid function normal.
(A flying disc containing a single eye with a vertical slit pupil glides out of the spacecraft and looks around.)
VISHINSKY: Launch attitude seven.
MORELLI [OC]: Seven.
VISHINSKY: Telesystems on transverse sweep.
MORELLI [OC]: Transverse sweep established.
(Salamar enters.)
VISHINSKY: Maintain ocular frequency.
MORELLI [OC]: Ocular frequency is transmitting now.
VISHINSKY: Oculoid tracker launched.
(A viewscreen shows an infrared image of the jungle.)

[Jungle]

(The Doctor and Sarah hear the tracker whirring as it bobs and weaves through the trees, and hide from it.)
SARAH: What was that, an elfin spirit of the forest?
DOCTOR: Some sort of surveillance device.
SARAH: Oh. At least we know we can't get lost.
DOCTOR: No. I met him once, you know.
SARAH: Who?
DOCTOR: Shakespeare. Charming fellow. Dreadful actor.
SARAH: Perhaps that's why he took up writing.
DOCTOR: Perhaps it was.

[Space probe command area]

SALAMAR: You've seen the body?
SORENSON: All my party died the same way. A type of total dehydration.
SALAMAR: I have the bio-analysis here. All the organs are undamaged. No contusions or evidence of pressure. Complete extraction of bodily fluids from tissue.
VISHINSKY: We've no weapon in our technology that could produce such an effect.
SALAMAR: No, a heat weapon would have produced external injuries. All the indications are that some very rapid form of freeze-drying occurred.
SORENSON: Isn't this irrelevant, Controller?
SALAMAR: Irrelevant?
SORENSON: I came to Zeta Minor to prove a theory that could save our civilisation. I've been successful. That's all that matters.
SALAMAR: Seven men have died at the hands of these aliens.
SORENSON: There is more at stake here than seven lives. Our solar system is dependant upon a dying sun. I've discovered a new and inexhaustible source of energy. Rock formations on the fringe of the universe.
MORELLI: Controller, the oculoid tracker has located the prisoners.
SALAMAR: Order out the pursuit party.
PONTI: Right, Controller.
SORENSON: You're wasting time. My mineral samples must be loaded aboard and we must prepare for immediate take off.
SALAMAR: I am well aware of your high position in the science authorities, Professor, but this is a military expedition with military objectives. The manual says hostile alien forces must be searched out and liquidated. That operation is now in hand.

[Rock pool]

(The Doctor and Sarah enter a rocky area with a black pool in the middle. The Doctor throws a stone into it but there is no splash, no ripples.)
DOCTOR: Yes, this is it.
SARAH: Is this where the thing lives?
DOCTOR: No, it doesn't live anywhere. It just is.
SARAH: Uh oh. Doctor.
(The oculoid tracker has found them.)
DOCTOR: Never mind about that. Look down there. What do you see?
SARAH: A pool.
DOCTOR: Look into it. Wouldn't you expect to see a reflection?
SARAH: There's nothing. What do you mean, this is it?
PONTI: Raise your hands over your heads. Search him.
DOCTOR: I can empty my own pockets, thank you.
PONTI: Put your hands over your heads.
DOCTOR: I've nothing up my sleeve, if that's what you mean.
PONTI: Search them both.
(A guard grabs Sarah from behind. She struggles and Ponti goes to search her. Suddenly he screams and falls backwards into the nothingness hole.)
DOCTOR: Get back! Didn't you learn anything? You're tampering with the balance of nature on this planet in ways you don't understand. It may already be too late.

[Expedition base]

SORENSON: I want these canisters loaded carefully.
DE HAAN: What's in them?
SORENSON: Refined ore. Energy. I calculate that six pounds of this material in our own solar system would produce heat equivalent to the output of our own sun over a period of three centuries. Well, don't you understand, man? Full scale exploitation of this planet would provide us with perpetual energy in any quantity whenever we needed it. I've made the greatest discovery in scientific history.
DE HAAN: Do you need any of this other equipment, Professor?
SORENSON: You still don't understand the implications, do you. No, no, there's nothing here. The base can be abandoned.

[Space probe command area]

VISHINSKY: The prisoners have cleared quarantine.
SALAMAR: Any weapons?
VISHINSKY: Our detectors revealed nothing. If they caused the deaths, they used some super-sensory process.
SALAMAR: It's not unknown for aliens to utilise such techniques. Bring them in.
VISHINSKY: Have the aliens brought in.
SALAMAR: Where's Sorenson?
VISHINSKY: Getting his samples aboard preparatory to launching.
SALAMAR: I've given no orders for a launching. There are seven deaths to be accounted for.
VISHINSKY: Sorenson has a lot of authority in high circles, Salamar. It may be unwise to antagonise him.
SALAMAR: He's still a civilian. Military priorities take precedence.
VISHINSKY: Bring the prisoners forward.
DOCTOR: Prisoners? We're here to help. We're not prisoners.
SALAMAR: You are prisoners, and you are charged with diverse acts of war against the subjects of Morestra.
DOCTOR: Not guilty.
SARAH: This is ridiculous.
VISHINSKY: Silence.
DOCTOR: Do you have any idea of what you're up against on this planet?
SALAMAR: You will not respond to questions with counter-questions.
DOCTOR: If you won't allow us
VISHINSKY: Silence! You will have a chance to speak, Doctor.
DOCTOR: Thank you.
SALAMAR: This interrogation will be conducted in an orderly manner. Failure to comply will result in your immediate execution.
(The Doctor opens his mouth but Sarah glares at him so he shuts it again.)

[Quarantine area]

(de Haan places Sorenson's mineral containers next to the Tardis.)
MORELLI: Radioactive reading just within our tolerance. What do they contain?
SORENSON: Mineral elements from the planet.

[Space probe command area]

SALAMAR: Yesterday, you were found with the body of one of our scientists. Last night one of our guards died and you were seen kneeling over him. Can you explain this?
DOCTOR: We had nothing to do with those deaths. They were brought about by your intrusion. Listen, now listen to me, please. Here on Zeta Minor is the boundary between existence as you know it and the other universe, which you just don't understand.
VISHINSKY: Other universe?
DOCTOR: Yes. From the beginning of time, it has existed side by side with the known universe. Each is the antithesis of the other. You call it nothing, a word to cover ignorance, then centuries ago scientists invented another word for it. Antimatter, they called it.
SALAMAR: Nonsense. Clever deception to cover their real motives.
VISHINSKY: I don't think so. Let him finish.
DOCTOR: And you, by coming here, have crossed the boundary into that other universe to plunder it. Dangerous.
SORENSON: Salamar. My mineral samples are aboard. It is getting dark. Prepare for the return journey.
DOCTOR: Mineral samples? Sorenson, you can't take any part of this planet with you.
SORENSON: That was the purpose of my expedition.
DOCTOR: But you can't!
SALAMAR: Get them out of here. I'll deal with them later.
DOCTOR: Sorenson, if you don't listen to me, you'll never leave this planet.
(The Doctor and Sarah are dragged away.)
SALAMAR: Now look, Sorenson. I'm aware of your position, but I am in command of this probe and I decide when it takes off. Do you understand?
SORENSON: What did he mean, we'll never leave this planet?

[Quarantine area]

SARAH: Do you ever get tired of being pushed around?
DOCTOR: Frequently.
SARAH: We could get in the Tardis and disappear.
(She pulls the key out of her pocket and the Doctor takes it.)
DOCTOR: No, no. It's tempting to let them go ahead and destroy themselves. The trouble is, they wouldn't be the only ones.
SARAH: How do you mean?
DOCTOR: Cataclysm.
SARAH: The Big Bang?
DOCTOR: Yes. The end of the universe.
(The Doctor opens one of Sorenson's canisters.)
SARAH: What's that?
DOCTOR: Do you remember the rocks around the pool?
SARAH: Mmm. They were sort of a brownish colour.
DOCTOR: This is a concentrated form.
(The Doctor scoops some out with the lid of an empty tin of Farrah's original Harrogate Toffees that he has in his pocket.)
SARAH: It's changing colour!
(Gold, green, red, gold. The Doctor puts them in the tin and replaces the lid.)
SARAH: What are you doing? What are you doing?
DOCTOR: It's just an idea.
(A noise starts up.)
SARAH: It's the compression units. They're preparing to launch!
DOCTOR: Fools. Do they really think they'll be allowed to leave with this on board?

[Space probe command area]

(The last of the guards return to the ship and the hatch closes.)
VISHINSKY: Pressurisation complete. Cyclostimulators activate.
MORELLI: Activated.
VISHINSKY: Power jets to lock in positions.
MORELLI: Locked.
VISHINSKY: Gyrostabilisers, activate.
MORELLI: Activated.
VISHINSKY: Prepare for final ignition. Ten, nine, eight
(The lights dim and an alarm sounds.)
MORELLI: Pressurisation falling. Cyclostimulators not responding.
SALAMAR: Activate secondary launch units.
MORELLI: Cycle complete.
VISHINSKY: Secondary launch units activated.
SALAMAR: I don't understand.
VISHINSKY: What's gone wrong?
MORELLI: Emergency power units inoperative. Main and secondary circuits failing.
SALAMAR: Cancel ignition.
VISHINSKY: It doesn't make sense.
SORENSON: Look!
(The energy creature is outside.)
SALAMAR: What is it?
VISHINSKY: It's going to attack the ship!
SORENSON: Energy. Pure energy in physical form. It's incredible!
VISHINSKY: Operate the forcefield barrier.
SALAMAR: Get the alien prisoners up here. I think that thing's got something to do with them.
MORELLI: The barrier won't work. There's not enough power!
SALAMAR: Get out there and stop it.
(A squad of guards rush out as the Doctor and Sarah enter. The guard's weapon's energy pulses go straight through the creature. It gets one of them.)
DOCTOR: You've sent those men to their deaths. Use the forcefield barrier.
VISHINSKY: It won't work.
DOCTOR: Then link it to the atomic accelerator.
MORELLI: It's too dangerous.
(Another guard dies.)
DOCTOR: Link the forcefield to the atomic accelerator!
VISHINSKY: We've got to try it, Salamar. Give the order!
SALAMAR: Do it.
MORELLI: Linked.
VISHINSKY: Forcefield barrier.
(The energy creature comes up against the forcefield and is pushed back. It fades away.)
VISHINSKY: Thank you, Doctor.
SALAMAR: All right, tell us what you know about that.
DOCTOR: Sorenson, you're a scientist. Surely you appreciate the dangers of moving material from one dimension to another.
SORENSON: That was the whole purpose of my expedition.
DOCTOR: You're tampering with hideously dangerous forces.
SALAMAR: But it's gone.
DOCTOR: Yes, for the moment. But while those mineral samples remain on board, it'll always come back.
VISHINSKY: Are you saying we can't take off?
DOCTOR: Unless you abandon those canisters, yes.
SORENSON: But we need those mineral samples.
DOCTOR: Why?
SORENSON: Our sun is dying. By taking material from this planet, we can refuel it and save our civilisation.
DOCTOR: I'm afraid that isn't the solution. You must find an alternative energy source.
SALAMAR: So if we jettison those canisters we can take off?
DOCTOR: As long as your intention to leave as you came, empty-handed, is made clear.
VISHINSKY: But how do we communicate that intention?
DOCTOR: Through me. I'm not entirely without influence, but it will take time.
SALAMAR: Very well. But the girl will stay here. You may go.
SORENSON: But
DOCTOR: Alone. I must go alone.
SARAH: Doctor.
DOCTOR: Yes, I know. I'll take care.
(The Doctor leaves.)
SALAMAR: Launch the oculoid tracker. I want his movements followed.

[Rock pool]

(The tracker watches as the Doctor stands at the edge of the hole. Then the energy creature slowly rises from the nothingness. The Doctor puts his hands to his head as the crackling starts, and he sways.)
DOCTOR: No!
(And everyone on the spacecraft watches in horror as he topples into the hole.)

Part Three

[Space probe command area]

SARAH: Doctor! Do something.
SORENSON: There is nothing to be done.
VISHINSKY: He has disappeared into the vortex between this universe and the next.
SARAH: No, not the Doctor! He can't be dead.
SORENSON: He has ceased to exist. Controller, it is nearly night. We must prepare to launch.
SALAMAR: I agree. Vishinsky, see the Professor Sorenson's mineral samples are removed.
SORENSON: No. No, you can't leave those canisters behind.
SALAMAR: Those minerals are endangering the safety of my command. They must be jettisoned.
SORENSON: You arrogant young fool. The whole purpose of your command was to get me and that positron material back to our cosmos.
(Sarah sneaks out, unseen.)
SALAMAR: So that you can be hailed as the saviour of civilisation? No, Professor. My orders were simply to find your party and get back.
SORENSON: If you abandon that material, you destroy years of my life's work.
SALAMAR: You are a civilian aboard a military vessel. There will be no further argument.
(Sarah makes her way through the jungle as the Doctor turns and falls through the nothingness of the void, until he comes face to face with the energy creature in its own reality.

[Quarantine area]

DE HAAN: Carry them in, carry them out. That ought to be the Space Service motto.
MORELLI: Yes, well, they've changed their minds.
DE HAAN: Yeah, well they could have changed their minds first, couldn't they? I mean, just for a change.
MORELLI: Listen, de Haan. The Controller simply wants us to take these canisters outside the take off forcefield area, right?
DE HAAN: Right.
MORELLI: Right.
DE HAAN: It's only another fifty yards multiplied by ten.

[Outside the quarantine area]

(Sorenson hides under the stairs from the quarantine area as Morelli and de Haan come out carrying canisters.)
DE HAAN: Half my service I spend flying one way, the other half I spend flying back again. They should pay me for staying in one place.
(Morelli and de Haan come down the stairs and out.)
MORELLI: Come on.
(Sorenson goes up the stairs and into the quarantine area. He picks up one of the remaining canisters, gives the Tardis a funny look, and leaves.)

[Rock pool]

SARAH: Doctor! Doctor! Doctor.
(A hand appears over the edge of the 'pool', then a second. She grabs it and helps the Doctor pull himself out. He is clutching his toffee tin.)
DOCTOR: Sarah, Vandervelt's equation of knowledge. Quite wrong.
(The Doctor collapses.)
SARAH: Doctor, come on. Come on. The spaceship, it's leaving. Doctor! Doctor! Doctor, wake up. Doctor!

[Space probe command area]

DE HAAN: All the canisters are off the ship, Controller.
SALAMAR: Good. We'll go for immediate take off, Vishinsky.
VISHINSKY: Commence pressurisation and pre-ignition checks.
REIG [OC]: Pre-ignition checks commenced.
SALAMAR: Recall the oculoid.
VISHINSKY: Cancel that!
SALAMAR: What?
VISHINSKY: The oculoid picture. Look!
(The viewscreen shows Sarah struggling with the unconscious Doctor.)
VISHINSKY: Cut the forcefield.
SALAMAR: Are you taking command, Vishinsky?
VISHINSKY: He's alive, Salamar.
SALAMAR: There are higher priorities than recovering corpses.
VISHINSKY: I'm going out for them.
SALAMAR: We must leave this planet before night. Prepare the sick bay.

[Sorenson's room]

(Sorenson stares into the open canister as the crystals change colour - green, blue, green, blue, red, blue, red, white.)
SORENSON: No.
(He sits and picks up a dictaphone.)
SORENSON: While still on the surface of Zeta Minor, and within the stable environment of the space probe, positron elements showed a twenty, a twenty percent increase in flux activity. This would seem to indicate a substantially greater, a greater, argh.
(Sorenson puts his head in his hands in pain. The crystals glow red as he stands, goes over to a mirror and uncovers his eyes. They are glowing red, like the crystals. He pours himself a glass of something that steams in normal air, drinks it, then looks again. His eyes have returned to normal.

[Sickbay]

(The Doctor is carried in on a stretcher, which becomes part of the diagnostic bed. De Haan plugs it in and hands the cortical monitor to Vishinsky, who fits it to the Doctor's head.)
VISHINSKY: Electro-function almost non-existent.
SARAH: But he's still alive.
VISHINSKY: Raise the stimulation intensity twelve degrees.
DE HAAN: But that's way over safety margins.
VISHINSKY: Do it!
(The Doctor twitches.)
SARAH: He moved!
DE HAAN: Don't expect too much.
SARAH: What?
DE HAAN: They often move under stimulation. It's the nervous system.
VISHINSKY: He's breathing.
SARAH: He's coming round. Doctor. Doctor?
SALAMAR [OC]: Stand by for take off. Vishinsky to command area.
VISHINSKY: He'll be all right. Stay with him.
SARAH: Vishinsky. Thanks for helping us.
(Vishinsky and de Haan leave.)

[Space probe command area]

MORELLI: Pressurisation complete, Controller.
SALAMAR: Activate cyclostimulators.
(Vishinsky takes his seat.)
MORELLI: Power jets locked in.
SALAMAR: Prepare for ignition. Take the countdown, Vishinsky.
VISHINSKY: If we don't make it this time, we never will.

[Sickbay]

(The Doctor wakes.)
SARAH: Doctor.
DOCTOR: What's the noise?
SARAH: You're all right. We're taking off.
DOCTOR: What? But the canisters. I promised.
SARAH: It's all right. They've been dumped. Your promise as a Time Lord? Well, what happened?
DOCTOR: It's difficult to explain.
SARAH: Well try. What did you do, enter another universe and have a chat with it?
DOCTOR: I communicated.
(The lights flicker and an alarm sounds.)
SARAH: We seem to be having trouble again.
(The Doctor takes his tin out of his pocket.)
DOCTOR Oh! Come on.

[Space probe command area]

VISHINSKY: We're not going to make it.
SALAMAR: Activate secondary boosters.
REIG [OC]: Secondary boosters activated.
VISHINSKY: The syncronisers are hitting red.
MORELLI: Gravity drag increasing.
SALAMAR: I want ten seconds of maximum fuel burn.
VISHINSKY: That's crazy! You
SALAMAR: You heard me. Ten seconds.
(The Doctor and Sarah enter.)
MORELLI: Gravity drag still increasing. Height only thirty miles.
VISHINSKY: That's more than gravity. There's antimatter still aboard!
SALAMAR: All the canisters were removed.
DOCTOR: Except for this.
SALAMAR: What's that?
DOCTOR: Antimatter. How else do you think I survived that pool?
SALAMAR: Is there enough there to hold us back?
DOCTOR: Yes.
SALAMAR: You idiot. Morelli, get that to the jettison hatch fast.
(Morelli grabs the tin and runs.)

[Space probe corridor]

(Morelli walks along, trance-like.)
DE HAAN: Hey, Morelli, when are we going to get some lights down here? Do you think the command area's the only place anyone's working?
(There is a crackling sound, then a strangled sound off screen.)
DE HAAN: Morelli? Morelli!
(De Haan runs down the corridor as Sorenson leaves Morelli's desiccated body.)
DE HAAN: Morelli.

[Space probe command area]

REIG: Height, two hundred miles.
VISHINSKY: We're in free space, but we're losing speed again.
SALAMAR: Drag is still increasing. I don't understand it.
DOCTOR: Then I suggest you search the ship.
SALAMAR: Oh? Why?
DOCTOR: Because there must still be antimatter aboard. It's the only explanation.
SALAMAR: Impossible.
VISHINSKY: Salamar, we're burning fuel at thirty units over norm. At this rate we'll never make the stellar systems.
SARAH: But that means we'll be marooned in space!
DOCTOR: If we're not vapourised first.
SALAMAR: Vapourised? What do you mean?
DOCTOR: Antimatter in collision with matter causes radiation annihilation. A release of energy more powerful than nuclear fission.
SALAMAR: There is no antimatter aboard this ship!
DOCTOR: And I tell you there is.
DE HAAN: Controller! Controller, Morelli's dead.
SALAMAR: Dead?
DE HAAN: He's been killed by some sort of an animal.
VISHINSKY: Animal?
DE HAAN: I saw it in sector three.
VISHINSKY: Restore all walkway lights. All right, de Haan, come on. Show us.

[Sorenson's room]

(Sorenson pours himself another 'cooling' drink.)
SORENSON: It's all gone so wrong.
(The intercom buzzes.)
SORENSON: Yes?
REIG [OC]: Report at once to sector three. Controller Salamar wants to see you.
SORENSON: What for?

[Sickbay]

(The desiccated corpse is being examined.)
DOCTOR: Well?
VISHINSKY: The pathology readout is identical to the others. Total dehydration. Even the bone marrow.
SARAH: But how could that thing get on board?
VISHINSKY: I don't know. The forcefield was operating all the time the hatch was open. It was phased to cut in automatically.
(The corpse is slid into a mortuary cupboard.)
DOCTOR: I wonder.

[Space probe corridor]

(The place where Morelli died is being scanned by de Haan.)
SALAMAR: You're a scientist. You must have formed some theory.
SORENSON: All the deaths appear to have been caused by a technology unknown to us. That would seem to implicate the Doctor and the girl.
SALAMAR: Why?
SORENSON: Well, they're aliens.
SALAMAR: But they were in the command area when Morelli was killed.
SORENSON: That machine in the quarantine berth might contain the answer.

[Sickbay]

(Vishinsky uses the intercom.)
VISHINSKY: Crew records. What denomination was Morelli?
DOCTOR: Can I see the printout?
VISHINSKY: Of course.
REIG [OC]: Morelli was Morestran Orthodox.
VISHINSKY: Oh, one of those.
SARAH: What are you doing?
VISHINSKY: Disposal procedure. We may have to play the last rites but we don't have to listen.
(He turns down the volume on the music. A hatch opens in the side of the spacecraft and a casket floats out to rest amongst the stars.)
VISHINSKY: Another good soldier gone to the greatest army of them all.
SARAH: Out into space to drift forever.
VISHINSKY: It's clean and tidy.
SARAH: It's horrible.
DOCTOR: Vishinsky, I'd like a medical check on everybody aboard the ship.
VISHINSKY: Why?
DOCTOR: Because someone is contaminated.
SALAMAR: Yes, Doctor, and we want to examine that space machine of yours.
DOCTOR: Why?
SALAMAR: We believe you to be responsible for all the deaths. Unless you cooperate, I shall kill you and the girl without compunction.
SARAH: Oh, great. That's the thanks you get for helping people.
DOCTOR: What is all this?
VISHINSKY: The Doctor risked his life on our account.
SALAMAR: That was a ruse to gain our confidence. His real intention is to destroy us.
DOCTOR: Why? For what reason?
SORENSON: There are other civilisations as desperate as we are for new energy sources. My discoveries on Zeta Minor would be of immense value to them.
DOCTOR: Professor Sorenson, has it ever occurred to you that you might be mistaken? That there is no practical method of exploiting antiquark energy?
SORENSON: Oh no, you're wrong. I've spent my life discovering alternative energy.
REIG [OC]: Controller Salamar. Calling the Controller.
SALAMAR: What is it, Reig?
REIG [OC]: We're in trouble, sir. The ship's stopped moving.
SALAMAR: That's impossible.

[Space probe command area]

REIG: Sir, the progress register has stopped. We're making no headway.

[Sickbay]

SALAMAR: I'm coming up. Professor, watch the girl. You, come with us.
(The space service men leave with the Doctor.)
SARAH: There's no need to. I'm not going to jump out, am I.
SORENSON: What is your friend's field of science?
SARAH: Oh, everything. He's brilliant.
SORENSON: And he's wrong. He has to be wrong. Antiquarks come in three configurations, exactly as I predicted. All my theoretical calculations have proved this! We shall find a way of discovering the energy!
SARAH: All right. I'm not arguing.

[Space probe command area]

VISHINSKY: We're stationary. Suspended in space.
SALAMAR: It's crazy. The thrusters are still at full power.
DOCTOR: The answer's really very simple. You've come to the end of your piece of elastic.
SALAMAR: What are you talking about?
DOCTOR: It won't stretch any further. In fact, very soon it will start to pull you back.
SALAMAR: Nothing can do that.
DOCTOR: Antimatter can. There's still some aboard and this proves it.
VISHINSKY: You mean the ship will be dragged back to Zeta Minor?
DOCTOR: Yes, faster and faster. Until, of course, we reach the surface, then we'll stop with a bang. The only way to prevent it is to find the antimatter.
SALAMAR: You're diverting attention from what's really causing the trouble. You! You and whatever's in that machine of yours. Something that's draining the power from this ship.
DOCTOR: Salamar, you're wrong again.
SALAMAR: We'll see. Vishinsky, take charge here.

[Sickbay]

SORENSON: Antimatter is simply matter composed entirely of antiparticles. Therefore, the hypothetical energy available, available, is, is stupendous.
(Sorenson clutches his head.)
SARAH: What's wrong? Are you all right?
SORENSON: Yes. Yes, I'm
(The crackling starts up and Sarah goes rigid. Sorenson staggers out of the room and she returns to normal.)

[Space probe corridor]

(De Haan is still scanning the floor plates when Sorenson walks past him. He goes up the stairs, then turns and comes back down again.)
DE HAAN: Oh, Professor, I
(De Haan looks horrified. Sarah hears his scream in Sickbay and runs out.)
DE HAAN: Argh!

[Quarantine area]

(The Doctor enters with his hands raised, followed by Salamar brandishing a hand weapon.)
DOCTOR: Usually I only entertain friends in the Tardis.
SALAMAR: Shut up. Open it.
DOCTOR: Externally, as you can see, it resembles a London police box.
SALAMAR: Open it!
(Sarah screams somewhere. Salamar turns, the Doctor grabs his gun arm and knocks him out with a punch, then leaves.)

[Space probe corridor]

(Sarah is watching the shadow of Sorenson's Hyde persona snarling over de Haan's body.)
DOCTOR [OC]: Sarah!
(The shadow leaves, and Sarah goes forward to find the desiccated remains on the floor.)
DOCTOR: Sarah, what happened?
SARAH: I caught a glimpse of that thing. It was horrible.
DOCTOR: Antiman.
SARAH: Antiman?
DOCTOR: A hybrid creature running amok.
SALAMAR: Don't move! De Haan. You've killed de Haan!
DOCTOR: Oh, now listen, Sa
(Salamar shoots the Doctor point blank.)
SARAH: Doctor!
(Vishinsky enters and tries to take Salamar's weapon.)
SALAMAR: No! They killed de Haan.
VISHINSKY: Some thing killed de Haan.
SALAMAR: Let's get rid of them before they kill us all. Take them to the ejector chamber. Hurry!
(Guards drag the Doctor away, and Sarah follows at gunpoint.
In his room, Sorenson takes another drink, but then knocks over the flask. Viscous red liquid pours out onto the floor. To a faint crackling sound, and with his eyes still glowing red, Sorenson crawls onto his bed.)

[Sickbay]

(A hatch opens in the side of the ship. The Doctor and Sarah are strapped into two mortuary units.)
SALAMAR: Prepare to eject.
SARAH: You can't do this! It's murder!
VISHINSKY: She's right. You have no evidence. You cannot do it.
SALAMAR: How much evidence do you want? The whole crew dead? Eject! Eject.
VISHINSKY: No, Salamar.
(The two men struggle. Salamar forces Vishinsky's arm down onto the handle that sets the process in motion, and the Doctor and Sarah slide out of sight.)

Part Four

[Space probe command area]

REIG: Maintain boosters at full thrust. We're only just holding rev. We must avoid being pulled into reverse.
(There is a crackling noise behind him. Reig turns and then calls into the intercom.)
REIG: This is the command deck! Send help! Argh!

[Sickbay]

REIG [OC]: Help! Argh!
(Salamar and Vishinsky stop fighting. Salamar leaves with the guards, and Vishinsky reverses the eject controls before following them. The Doctor and Sarah slide back into view.)

[Space probe command area]

SALAMAR: Reig!
(A desiccated corpse lies over Reig's console.)
VISHINSKY: Reig. If we hadn't been wasting our time down there.
SALAMAR: They caused it all.
VISHINSKY: How could they have caused this? We were with them. (into intercom) Attention. All crewmen report to assembly point immediately. Red alert! Red alert!
SALAMAR: Countermanded. Only I can give a red alert.
VISHINSKY: It's too late for any more mistakes, Salamar. I'm taking command.
SALAMAR: You'll regret this.

[Sickbay]

(Sarah and the Doctor have freed themselves and are climbing out of the mortuary trays. The Doctor is still groggy.)
DOCTOR: Where've they gone?
SARAH: I think there's been another killing.
DOCTOR: What?
SARAH: Doctor. Doctor, it is that thing from the planet. I felt it.
DOCTOR: You what?
SARAH: Just before de Haan was killed, I felt the same sort of icy suction.
DOCTOR: Who was with you?
SARAH: Professor Sorenson.
DOCTOR: Sorenson. Of course. The sole survivor of the expedition.
SARAH: So Sorenson is Antiman.
DOCTOR: Yes. He's been infected with antimatter. His brain cells are being destroyed. He'll descend to the level of a brute. Sarah?
SARAH: Yes?
DOCTOR: Get to command deck. Tell them to shut down all the hatches. Our only chance is to keep it isolated.
SARAH: Right. But what are you going to do? Doctor!
DOCTOR: Do as I say.

[Space probe command area]

VISHINSKY: Command area to solarium section. Who's in charge there?
RANJIT [OC]: Senior crewleader Ranjit, sir.
VISHINSKY: Ranjit? Good. You know why we're on red alert?
RANJIT [OC]: They say we picked up some contagion back on the planet.
VISHINSKY: We picked up something. Some animal. It's killed Morelli, Reig and de Haan, so take no chances. Keep your men on full alert and await further orders.
RANJIT [OC]: Right, sir.
SALAMAR: What are you going to do now, Vishinsky? Look at the course monitor. We're heading back to Zeta Minor. Come on, you've taken charge. Give an order. Give an order that'll stop us crashing, or we're all going to die.
VISHINSKY: Keep your nerve, Salamar.
(Sarah enters.)
VISHINSKY: Where's the Doctor?
SARAH: I don't know, but he said you've got to close all the hatchways immediately.
VISHINSKY: As soon as Professor Sorenson reports in.
SARAH: No, now! Don't wait for Sorenson. The Doctor says he's behind all this.
SALAMAR: That's insane. How can he be?
SARAH: Something on the planet affected him. Look, you've got to shut the hatchways before it's too late.
SALAMAR: It's another trick.
VISHINSKY: The Doctor's been right so far. We should have listened to him before. Close all section hatchways!
(Bulkheads come down in the corridors, sealing them into small compartments.)

[Sorenson's room]

(The Doctor uses his sonic screwdriver to unlock the door, and enters carefully. He opens the container on the desk then puts the lid on it again. He is about to leave when he notices the flask by the mirror. After picking it up and sniffing it, the Doctor opens the container again and spoons out some pulverised crystal, then pours a few drops of the red liquid onto it. The crystals glow brightly for a few moments then turn a dull brown. The Doctor reseals the container as Sorenson enters behind him.)
DOCTOR: Keep away!

[Space probe command area]

SARAH: And the antimatter has turned Sorenson into that monster.
VISHINSKY: It's incredible. Sorenson?
(Salamar runs up the steps and takes a unit from a conduit running up the wall.)
VISHINSKY: Salamar!
(Salamar pulls his weapon out.)
SALAMAR: Keep away!
VISHINSKY: Don't be a fool.

[Sorenson's room]

(The Doctor brandishes the container like a weapon.)
DOCTOR: Keep away.
SORENSON: I require an explanation.
DOCTOR: Professor Sorenson, you're ill.
SORENSON: What do you mean, ill?
DOCTOR: You think you've discovered an oral vaccine to protect you against antiquark penetration, but you're wrong.
SORENSON: It worked.
DOCTOR: For a time, but it set up a cycle of chemical change. There's no way back, Sorenson. You've reached the point where your tissues are so monstrously hybridised that the next metabolic change could be the final one.
SORENSON: No.
DOCTOR: There isn't much time.
SORENSON: No!
DOCTOR: You and I are scientists, Professor. We buy our privilege to experiment at the cost of total responsibility.
(The Doctor hands Sorenson the container.)
SORENSON: The hypothesis was false.
(Sorenson leaves.)

[Space probe command area]

SALAMAR: Open the hatch!
VISHINSKY: Take the shielding off that neutron accelerator, you'll be dead in minutes.
SALAMAR: But I'll take Sorenson with me. You'd like that, wouldn't you, Vishinsky? That might save your life. You'd like to live?
VISHINSKY: You're out of your mind.
SALAMAR: Oh, no. No, this is leadership. Strong action. That's why I'm Controller. Open that hatch!
(A guard moves forward and Salamar shoots him.)
SALAMAR: Now, open it!
SARAH: Let him go, Vishinsky. Let him go!
(Vishinsky goes to Reig's console and presses a button.)
SALAMAR: You, Controller? You haven't a hope.
(Salamar leaves.)
VISHINSKY: If Sorenson doesn't get him, the radiation will.

[Sickbay]

(Sorenson staggers in and puts the container in a mortuary tray. Then he lies down in the other and reaches for the eject handle. But the hand is no longer human, and it does not push it down. Meanwhile, Salamar heads for the quarantine area. A little later, the Doctor enters the sickbay and sees the container. The intercom beeps.)
VISHINSKY [OC}: Command area calling.

[Space probe command area]

DOCTOR [OC]: This is the Doctor.
VISHINSKY: Doctor, we're accelerating back to Zeta Minor. Have you located the antimatter?

[Sickbay]

DOCTOR: Listen, Vishinsky. Listen. There are now two forces of antimatter aboard. I've got one, and the other one is Sorenson himself.

[Space probe command area]

SARAH: But Salamar's out hunting Sorenson now.
VISHINSKY: With a neutron accelerator.

[Sickbay]

DOCTOR: He's got to be stopped. How long to impact?
VISHINSKY [OC]: Less than thirty minutes.
DOCTOR: Keep the hatchways open.
(The Doctor leaves with the container.)

[Quarantine area]

(Something crackles and croaks in the room.)
SALAMAR: Come on! Come on out and face me!
DOCTOR [OC]: Salamar!

[Space probe corridor]

DOCTOR: Where are you, Salamar? Don't use the accelerator. Salamar!

[Quarantine area]

DOCTOR [OC]: Where are you? Salamar! Whatever you do, don't use the accelerator!
(But Salamar opens the shielding on the unit as the devolved Sorenson attacks him.)
DOCTOR [OC]: Salamar!
(Sorenson knocks Salamar down, and gets the full glow of the neutron accelerator. By the time the Doctor enters, Salamar has been desiccated. The Doctor closes the shielding, takes Salamar's weapon, the accelerator and the canister, and goes to the intercom.)
VISHINSKY [OC]: Command area.
DOCTOR: Vishinsky, it's too late. Salamar's dead.

[Space probe command area]

DOCTOR [OC]: He used the neutron accelerator. If he hit Sorenson, it could be disastrous.
SARAH: You mean things can get worse? I don't believe it.
DOCTOR [OC]: Keep the hatches open. I'm coming up.
(Out in the corridor, the Doctor is confronted by two energy creatures. He waves the canister at them and they back away, then try to confront him again further along.)
SARAH: Oh, why is he taking so long?
VISHINSKY: I'll try the quarantine area again. Doctor. Doctor, if you can hear me, indicate your position.
SARAH: Something's happened to him. Doctor, are you all right?
(Someone or something bangs on the door on the upper level.)
DOCTOR [OC]: Open up, Vishinsky. Open up!
(The Doctor enters.)
DOCTOR: Shut down all the hatchways. It may hold them.
SARAH: Them?
DOCTOR: Yes, them. They've multiplied.
(Vishinsky puts the neutron accelerator back where it belongs. Meanwhile, an Antiman walks through a bulkhead. They watch the progress on a diagram of the probe on the monitor.)
SARAH: Doctor, look. The hatchways are going.
VISHINSKY: What are they?
DOCTOR: Duplicates of Sorenson. Pure antimatter. The neutron accelerator boosted its power, and the creatures split off and multiplied.
VISHINSKY: They're going towards the solarium chamber. Ranjit, what's happening? Can you hear me?
RANJIT [OC]: They're attacking. We need help! They're coming through! Argh!
VISHINSKY: Seven men. Sixteen minutes to impact.
SARAH: How can we stop them?
VISHINSKY: Acceleration thirty STS. Fifteen minutes.
SARAH: Doctor, what are we going to do?
DOCTOR: Stay here with Vishinsky, Sarah. I'm going out now and I may be some time.
VISHINSKY: Acceleration fifty STS. Fourteen minutes.

[Quarantine area]

(Using the antimatter container as a shield, the Doctor returns.)
DOCTOR: Sorenson? Sorenson.
(He wards off three antimatter creatures then Sorenson himself comes from behind the Tardis, looking very Mister Hyde. The Doctor uses Salamar's weapon to knock him down, unlock the Tardis and drag him inside. The Tardis dematerialises. The Doctor secures Sorenson's hands and feet in a rigid shackle before he wakes.)

[Space probe command area]

VISHINSKY: Acceleration seventy three STS. Eight minutes.
(Four Antimen are still walking through bulkheads. Vishinsky returns from looking outside the area.)
VISHINSKY: They're all around us. Come on, I'll need your help.
SARAH: We've only six minutes. Where are we going?
VISHINSKY: To get the forcefield equipment. If we can lay a band around the command area we may be able to keep them out.
(In the Tardis, Sorenson starts to bend the shackles like plasticine.)

[Forcefield equipment cupboard]

VISHINSKY: Take that. I'll bring the control box.
(Two Antimen appear.)
VISHINSKY: Back, quickly!

[Space probe command area]

VISHINSKY: Direction them in a line straight across. We'll seal off the area.
(They lay out the projectors. Smoke starts to come from the upper level hatch.)
SARAH: Look!
(An Antiman comes through. In the Tardis, Sorenson has freed himself and comes after the Doctor. The Doctor has landed the Tardis by the rock pool on Zeta Minor, and lures Sorenson out. They struggle by the hole. Now two Antimen have entered the command area and are coming down the steps towards the forcefield projectors. On the planet, Sorenson is finally toppled into the hole. The Doctor throws the canister of antimatter in after him. The Antimen vanish.)
VISHINSKY: Thirty seconds. Look, we're slowing down. Twenty five seconds. We've stopped. We're still on full power.
SARAH: We're moving again.
VISHINSKY: We're gaining height! We're moving away from the surface! The Doctor has done it!
SARAH: Yes, but where is he?

[Rock pool]

(A normal human being is lying beside the hole.)
DOCTOR: Sorenson. Professor Sorenson.
(He helps the dazed man into the Tardis and it dematerialises as the big energy creature emerges from the hole.)

[Tardis]

SORENSON: Where am I? What am I doing here?
DOCTOR: You're a very lucky man, Professor. You've been released.
SORENSON: Released?
DOCTOR: Yes. Because I kept my promise and returned the antimatter.
SORENSON: This isn't the Morestran probe ship.
DOCTOR: Don't you worry, Professor. Just rest a while. Everything's going to be all right.)
(The Tardis materialises back in the quarantine area.)

[Space probe command area]

VISHINSKY: We're making good progress now. Once we cross the galactic frontier we can signal for an emergency refuelling.
SARAH: Doctor!
VISHINSKY: Professor Sorenson! Are you all right?
SORENSON: Yes. Yes, I remember now. My researches. I've discovered a new source of energy.
DOCTOR: No, no, no, Professor. I think you'd abandoned that line. You'd decided to concentrate on deriving energy from the kinetic force of planetary movement.
SORENSON: Had I?
DOCTOR: Yes. Large source of untapped energy there.
SORENSON: The kinetic force of planetary movement. What a brilliant idea!
SARAH: Goodbye, Vishinsky. And thank you.
(Sarah hugs Vishinsky.
VISHINSKY: Goodbye. Goodbye, Doctor.
DOCTOR: Goodbye, Vishinsky. Come on, Sarah. We've an appointment in London and we're already thirty thousand years late.