[Bridge]

APRIL: No matter where I've travelled in the galaxy, Jim, this bridge is more like home than anywhere else.
KIRK: Yes, Commodore, I know the feeling.
APRIL: To me she was always like my child. I was there in the San Francisco Navy Yards when her unit components were built.
(McCoy enters with Mrs. April)
MCCOY: Jim, I didn't realise how many of the tools I use in Sickbay were designed by Sarah.
SARAH: As the first medical officer aboard a ship equipped with warp drive, I'm afraid I had to come up with new ideas all the time.
KIRK: Your modesty is unnecessary, Mrs. April. Your achievements as a pioneer doctor in space are well known.
MCCOY: And it's nice to know the lady is as intelligent as she is beautiful. Much like the flower she carries.
SARAH: Oh, Doctor, flattery will get you everywhere. But I'm afraid my flower is dying.
KIRK: It's a native of Capella Four, isn't it?
SARAH: Yes, but it has a life span of only a few hours. This morning it was a seedling, within a few hours it will be dead.
SPOCK: Excuse me, Captain. You asked to be notified when we made visual contact with the Beta Niobe nova.
KIRK: Thank you, Mister Spock. Mrs. April, you're about to see another of the galaxy's most beautiful sights, the Beta Niobe's supernova.
(A glowing ring doughnut is on the viewscreen)
SARAH: It is beautiful, but also very deadly.
SPOCK: We're travelling at a safe distance from the nova, Mrs. April.
APRIL: Beta Niobe. You were present when the star first started its explosion, Jim.
KIRK: Yes, we were, Commodore.
SPOCK: Captain, sensors are picking up an unidentified object travelling at an incredible speed, presently on collision course with the Enterprise.
KIRK: Put the ship on Red Alert. How fast is it travelling, Mister Spock?
SPOCK: At a speed that should be impossible to achieve. Something on the order of warp thirty six.
APRIL: No natural object has ever been recorded as travelling at that speed.
SPOCK: I believe it is not a natural object, but a ship.
KIRK: But who would have the technology to build a ship that could travel at such a speed?
SPOCK: No known race, Captain. Nevertheless, it will contact us in one point four minutes.
KIRK: Hard about, helmsman. Change course for twenty four mark seven.
SPOCK: Correction, Captain. The ship was on a collision course only by coincidence. It is apparently heading for the heart of the Beta Niobe nova.
KIRK: That's a course of self-destruction. Lieutenant Uhura, open hailing frequencies. I want to talk to that ship's captain.
UHURA: Captain, that ship is not responding.
KIRK: All right, if they won't talk, we'll slow them down. Mister Sulu, put a tractor beam on that ship.
SULU: Tractor beam on and operating, Captain.
AREX: We're having a small effect on other ship's speed, Captain. It has dropped to a speed of warp thirty two.
UHURA: Captain, they are making visual contact.
KIRK: Put it on the screen, Lieutenant.
(A blonde woman appears. She speaks, but the sounds are unintelligible. Then the picture fades)
KIRK: I've never heard that language before.
APRIL: Nor I.
KIRK: Run that message through the universal translator, Lieutenant Uhura. Perhaps it can tell us what language she is speaking in.
UHURA: Captain, the universal translator has the answer. The woman is speaking the same universal language we speak, but she is speaking in reverse.
KIRK: Lieutenant, let's hear that tape backward, which should sound forward to us.
UHURA: Yes, sir, on the screen.
KARLA [on viewscreen]: I am on a priority mission. Your beam is slowing my progress. Release my ship at once or I am doomed.
KIRK: Open hailing frequencies again, Lieutenant. Tell her she is endangering her life if she remains on her present course.
UHURA: No use, sir. She's refusing to answer.
SCOTT [OC]: Captain.
KIRK: Yes, Scotty, what is it?
SCOTT [OC]: Captain, the engines are buckling. We cannot keep up at this speed.
KIRK: Mister Arex, what is our speed?
AREX: Now at warp eleven, Captain.
KIRK: Mister Spock, how long until the alien vessel makes contact with the Beta Niobe nova?
SPOCK: Three minutes forty two point seven seconds.

[Engineering]

KIRK [OC]: Give me three and a half minutes, Scotty.

[Bridge]

AREX: Still increasing speed, Captain. Warp fourteen. Warp fifteen.
KIRK: I have no choice. I have to release the tractor beam. I can't destroy this ship and four hundred and thirty people to save one person. Mister Sulu, release our beam.
SULU: Sir, I can't release the tractor beam.
KIRK: What do you mean, Mister Sulu?
SULU: Our controls are inoperative. The ship isn't responding like it should.
KIRK: Go to manual override.
SULU: NO responding, sir.
KIRK: We've got to release that beam, or we're going to follow that ship into the nova!
SPOCK: Our speed is now warp twenty, and the other ship will contact the nova in one minute fifty eight point three seconds.
KIRK: I'm sorry, Commodore, Mrs. April. It looks as though we may not reach Babel.
APRIL: As starship personnel, we were always prepared to give our lives, Captain.
SARAH: We are still starship personnel, Captain.
KIRK: There's still one chance. After that ship enters the nova, it should burn up and break contact with our tractor beam. Mister Spock, how long will we have to apply full braking power and execute course change?
SPOCK: We are up to warp twenty two and increasing, Captain. We shall have forty two point eight five seconds to correct our course after the alien ship enters the nova.
KIRK: You heard that, Mister Sulu.
SULU: Aye, aye, sir.
KIRK: Mister Scott, we're going to apply full braking power in a minute.

[Engineering]

SCOTT: Aye, Captain. Our engines are almost gone.

[Bridge]

SCOTT [OC]: They've only lasted this long at this speed because the alien vessel is pulling us with our own tractor beam.
SPOCK: The alien vessel will contact Beta Niobe in fifty two point three seconds, Captain.
SPOCK: Contact in thirty nine seconds. Thirty eight, thirty seven
SPOCK: Thirteen, twelve, eleven
KIRK: Get ready to execute course change, Mister Sulu.
SULU: Yes, sir.
(The little ship enters the nova)
KIRK: Now, Mister Sulu!
SULU: Something's wrong, Captain. We're still being pulled by the alien ship.
KIRK: Impossible. It should have been destroyed instantly.
AREX: Apparently it was not, Captain. Our tractor beam is still connected to her.
SPOCK: And we are still increasing speed. Contact with the nova in thirty five point one eight seconds.
KIRK: That other ship may have been able to survive the heat of a nova, but the Enterprise can't. Mister Scott, how about that full braking power?

[Engineering]

SCOTT: We're as badly off as before, Captain. We have no control of the ship as long as that alien lassie has us in tow.

[Bridge]

SPOCK: Contact in twenty seconds.
KIRK: Keep trying those controls, Mister Sulu.
SULU: Still no change, Captain.
KIRK: It's got to work.
(Kirk Fiddles with Sulu's switches)
SPOCK: Fourteen seconds, thirteen, twelve
KIRK: Never mind, Mister Spock, it's no use.
(Sarah's flower shrivels in her hand. The Enterprise enters the nova and gets surrounded by sparkles)
KIRK: We're still here. Lieutenant Uhura, can you get us a visual?
(The viewscreen is white with black dots)
APRIL: What?
KIRK: Where are we?
(The Enterprise is sailing serenely through this reverse negative universe - backwards)

Captain's log, stardate 6770.6. The Enterprise has passed into the most alien landscape I have ever seen. We are in some reverse universe where black stars shine in a white void. We are still in the tow of the alien ship, both of us having survived the extreme heat of the Beta Niobe nova.

[Bridge]

SCOTT [OC]: This is Scott calling the Captain.
KIRK: Yes, Scotty. How are we doing down there?

[Engineering]

SCOTT: Well, we just had to learn to run the ship all over again. Every control is working in reverse.

[Bridge]

KIRK: All right. Lieutenant Uhura, we're going to contact that ship again. We need some answers.
SARAH: Captain Kirk. The Capellan flower!
APRIL: I'm sure Captain Kirk has other problems besides your flower, dear.
SARAH: You don't understand. Before we entered this universe it was about to die. and now it's in full bloom again.
KIRK: How's that possible?
SARAH: It's as if it were growing younger again. I can almost feel it while I'm holding it.
SPOCK: Captain, the flower is not the only thing on board that is growing younger.
KIRK: Explain, Spock.
SPOCK: Ship's chronometers are also running backward. The flow of time is reversed in this universe. The longer we stay here, the younger we will become.
(Sarah's flower becomes a seed)
UHURA: The alien ship is responding to our call, Captain.
KARLA [on viewscreen]: Your interference almost cost me my life.
KIRK: I can understand her now, without the aid of the universal translator.
SPOCK: Apparently our brains are also working in reverse, Captain, so we can now understand her language. That is why the ship seems to be operating in the reverse to us.
KIRK: I'm Captain James T Kirk of the USS Enterprise. We tried to prevent you from entering the Beta Niobe nova. We assumed your ship would burn up.
KARLA [on viewscreen]: I had to return to my own universe, Captain Kirk.
KIRK: Who are you? How did you come to be in our universe?
KARLA [on viewscreen]: I am an explorer of space. I was caught unaware when Amphion, previously a dead star, went nova and came to life. I was pulled into the star. But instead of burning up, I passed into a universe where everything operates in reverse to my universe.
KIRK: Our universe.
KARLA [on viewscreen]: Yes. My theory is that two stars going nova in the same place in both universes created a gateway which I passed through.
APRIL: In her universe, a nova is a dead star which comes to life! And when the explosions of a nova in her universe and one in our universe occur together, it's possible to travel between the two universes.
KIRK: Then we must return the same way, through the two novas.
KARLA [on viewscreen]: That would be impossible, Captain. Amphion is no longer nova. It has begun it's life as a star. I suggest you set a course to follow my ship. Perhaps our scientists can help solve your problem.
KIRK: We have little choice.

Captain's log, supplemental. We are proceeding to Karla Five's planet, Arret.

[Briefing room]

KIRK: Gentlemen, I'm sure none of us mind growing younger instead of older for a change.
APRIL: It pleases me, Jim. If we stay here long enough, I'll no longer be at the mandatory retirement age.
KIRK: Nevertheless, we must return home and I am open to suggestions.
SPOCK: It is logical that we must reproduce the conditions that brought us here. Two novas must occupy the same space in both universes in order to create a gateway for us to travel through. One star dying in our universe, and one being born here would recreate the correct conditions.
APRIL: That would take a remarkable coincidence, Mister Spock.
UHURA [on monitor]: Captain, we are approaching Arret. Karla Five is asking if you are prepared to beam down to the planet.
KIRK: Tell Karla Five that Mister Spock, Commodore April and myself will be beaming down.
UHURA [on monitor}: Yes, sir.

[Transporter room]

SCOTT: Karla Five has given us coordinates to beam down to her son's laboratory, Captain.
KIRK: Her son? We don't have time for children's games right now, Scotty, but beam us down.
SCOTT: Aye, sir.

[Laboratory]

(There is a baby in a playpen, and a man at a computer console)
KARLA: May I introduce my son, Karl Four.
KARL: (the man, of course) My honour to meet you, gentlemen.
SPOCK: Most logical. If the flow of time is reversed, then one is born at an old age, and dies in infancy. Your descendants are born before you, and your ancestors are born after you.
KIRK: Then the young child in the playpen
KARLA: My father, Captain.
KIRK: We could remain forever awed with the differences between our universes, Karla Five, but we must discover a way to return to our positive matter universe.
KARL: Exactly the problem I have been working on since Karla informed me of your troubles, Captain Kirk. This is a map of our galaxy. Our home solar system is here. You entered our universe through the Amphion nova, here. (the opposite arm of the galaxy)
KIRK: We need to coordinate this to our own universe. Can we do that, Spock?
SPOCK: Yes, Captain. Apparently the two universes occupy the same space, but in different dimensions.
APRIL: Assuming Beta Niobe and Amphion occupy the same space, we can determine if there are any other novas occupying the same space in both universes.
SPOCK: Correct, Commodore. Now if you'll watch the star map, you'll see the Milky Way. Here is Beta Niobe, and here is Earth. It corresponds exactly with Arret. By superimposing both star maps, we will see where two stars occupy the same place in both universes. The red spheres indicate where two stars are in the same space. No pair are novas in both universes.
APRIL: If stars begin as dead stars here then we could bring one of them to life prematurely.
KIRK: Yes, we could act as a midwife giving birth to a star. Then we would have two novas in the same position and theoretically return home.
KARLA: But I had to pass through the novas at my ship's top speed to avoid burning up. Your ship isn't capable of such a speed.
SPOCK: That's true, Captain.
KARLA: You are welcome to use my ship, Captain.
KIRK: I have a crew of four hundred and thirty, Karla Five. Your ship is suitable for only a few people.
SPOCK: We can't use her ship to transport us, Captain, but we could use it as an unmanned ship with our tractor beam attached.
APRIL: It could work. That's how we arrived here in the first place.
KIRK: It should work, yes. But any miscalculation anywhere along the way and we'll be plunging tail first into a supernova.

Captain's log, stardate 6770.1. Time continues to flow backward for us. We have set course for a dead star in this anti-matter universe that corresponds with the nova Minara in ours. We're being pulled by Karla Five's unmanned vessel, which is equipped with enough positive matter armament to ignite the dead star into life.

[Bridge]

KIRK: we just might get you to Babel after all, Commodore.
APRIL: I'll be glad to get home, but not necessarily to Babel. It only means the end of my career, Jim.
UHURA: Message coming in from Arret, Captain.
KARLA [on viewscreen]: I want to wish you luck, Captain. Whether you succeed or fail, the outcome will remain unknown to me.
KIRK: Yes, Karla Five. We'll burn to a crisp or escape into our own universe. Either way, you'll never hear from us again. Thank you for the sacrifice of your vessel.
KARLA [on viewscreen]: It is a small sacrifice, Captain Kirk. Success.
SULU: Tractor beam working properly, Captain.
AREX: We're meeting the speed of Karla Five's unmanned vessel, Captain.
KIRK: How much time before the youngest crew member returns to the time of birth?
SPOCK: Eighteen minutes thirty seven seconds in real time. But long before that we shall all be children. And, Captain, that also means we are losing our knowledge at an alarming rate. It is possible we will soon be unable to operate the Enterprise.
KIRK: How is our course, Mister Sulu?
SULU: I don't know. What am I doing here? What is all this equipment?
SPOCK: He's too young, Captain.
KIRK: Mister Arex, take over for him. Lieutenant Uhura, report to navigation console.
UHURA: I'm sorry, sir, I don't understand all this equipment. What do I do with these controls?
KIRK: Never mind. Spock, can you fill in for Sulu and Uhura?
SPOCK: Yes, Captain, but who will fill in for you?
KIRK: What do you mean?
SPOCK: At what age did you become a starship captain? And when did you enter Starfleet Academy?
KIRK: I see what you mean.
SPOCK: As a Vulcan, I age the slowest. I will be capable of assuming command longer than anyone else. But even I will become too young to know what to do.

Captain's log, supplemental. We have eleven minutes of real time left to reach the dead star, but all around my crew are turning into children, unable to operate the ship.

[Bridge]

(Kirk looks like he's not old enough to shave, April is middle-aged and Uhura's feet don't reach the floor any more)
SPOCK: Ten minutes fourteen point twenty one seconds, Captain. We shall arrive with only moments to spare. We will need to disconnect the tractor beam at the appropriate time.
KIRK: Tractor beam? How do we do that, Spock?
SPOCK: Captain, I must assume command. You are no longer able to command the Enterprise.
KIRK: Whatever you say. What shall I do?
APRIL: Mister Spock, as long as I am aboard, I am senior officer. I hate to pull rank, but you will be capable of command only for a few minutes, not long enough to complete the manoeuvres necessary to take us home.
SPOCK: You are correct, of course. Commodore April, command is yours.
APRIL: Commodore? I'm Captain April, Mister Spock.
SARAH: (now a vibrant red head) Robert, we're the only adults on the bridge. They're all teenagers and children.
APRIL: Make sure no harm comes to them, Sarah. We have to ignite that dead star if we're going home. Mister Spock, you are still capable of following orders?
SPOCK: Yes, Captain.
APRIL: Very good. Assume your post at the navigation console.
SPOCK: The dead star is directly ahead, Captain, twelve degrees south of galactic plane.
APRIL: Arm Karla Five's vessel, Spock.
SPOCK: Vessel armed, Captain. Nine seconds to impact. Eight, seven,
(The two ships rush towards the star)
SPOCK: Three, two
APRIL: Hang on, we're going right into the heart of the nova.
(Kaboom, sparkles, and Enterprise flies out of an expanding gas cloud, the right way around)
APRIL: We did it! We're home again! We're all right. We're home. The reverse aging process has stopped.
SARAH: But the Enterprise crew, they're all children.
APRIL: They can enter the transporter. It retains a memory of their original molecular structure.
SARAH: But what about us? We don't have to use the transporter. We can remain young, live our lives over again. You could command a starship once more.
APRIL: What a blessing to be able to live one's life over again, if the life you've led has left you unfulfilled. No Sarah, I don't want to live it all over again. I couldn't improve one bit on what we've had together.
SARAH: Oh, Robert.
(They embrace and kiss)
(Later, everyone is back to how they were at the start of the show)
KIRK: We've received a message from the Federation that might bring you some cheer. Lieutenant Uhura, would you relay it to Commodore April and his wife?
UHURA: In view of Commodore April's heroic actions aboard the USS Enterprise this stardate, we are reviewing his mandatory retirement, and will consider his appeal to remain Federation Ambassador at large.
APRIL: Well, good. Just because someone is seventy five years old doesn't mean they're ready to stop giving service to the galaxy!
SULU: Arriving at Babel in one hour fifteen minutes, Captain.
KIRK: I see your flower has blossomed again.
SARAH: Yes, our trip into the negative universe gave it a second life. It gave all of us a second life.