KIRK: Earth-style distress signal. SOS.
FARRELL: I've answered it on all frequencies, sir. They don't reply.
SPOCK: Not a vessel, a ground source. The third planet in this solar system, according to my instruments.
FARRELL: Directly ahead. Definitely an Earth-style signal.
KIRK: We're hundreds of light years from Earth, Mister Spock. No colonies or vessels out this far.
SPOCK: Measuring the planet now, Captain. It's spheroid-shaped, circumference twenty four thousand eight hundred seventy four miles. Mass six times ten to the twenty first power tons. Mean density five point five one seven. Atmosphere oxygen, nitrogen.
RAND: Earth!
KIRK: Not the Earth, another Earth. Another Earth?

Captain's Log, stardate 2713.5. In the distant reaches of our galaxy, we have made an astonishing discovery. Earth type radio signals coming from a planet which apparently is an exact duplicate of the Earth. It seems impossible, but there it is.

[Bridge]

KIRK: Hold us in a fixed orbit, Mister Spock.
SPOCK: Affirmative, Captain.
KIRK: Still no response, communications?
FARRELL: None, Captain.
KIRK: We'll beam down. Alert security. Prepare to transport landing party to surface. We'll land in the vicinity of the distress signals now being received.

[Street]

KIRK: Identical. Earth, as it was in the early 1900s.
SPOCK: More the, er, mid-1900s I would say, Captain, approximately 1960.
RAND: But where is everybody?
SPOCK: Readings indicate that natural deterioration has been taking place on this planet for at least several centuries.
RAND: You mean there's no one alive?
SPOCK: Not conclusive, Yeoman. The evidence would suggest that the distress signal is automated.
MCCOY: Now, this is marvellous. the most horrible conglomeration of antique architecture I've ever seen.
KIRK: Mister Spock. (comes upon child's tricycle)
TEENAGER: Mine! Mine! (attacks McCoy) Mine! Mine! Mine! Mine! Mine! Mine! (Kirk drags him off and hits him several times) It's, it's broke. Somebody broke it. Fix. Somebody, please fix.
MCCOY: Of course somebody will fix it.
SPOCK: Definitely humanoid, in spite of the distortion.
KIRK: But with the mind of a child. Bones, what is it?
MCCOY: A seizure of some type.
KIRK: We want to help you.
TEENAGER: Liar! Fibber, fibber, fibber, fibber, fibber, fibber, fibber!
MCCOY: It's dead. It's incredible.
KIRK: What is?
MCCOY: Its metabolic rate. It's impossibly high as if it's burning itself up, almost as if it aged a century in just the past few minutes.
KIRK: (sound of running) Come on!

[House]

KIRK: How old is this thing?
SPOCK: About three hundred years.
KIRK: (sound in the closet) Come out. We mean you no harm. (opens door)
MIRI: Don't hurt me, please.
KIRK: I'm not going to hurt you.
MIRI: No, please, don't. I didn't do anything.
KIRK: I won't hurt you.
MIRI: No, please don't.
KIRK: I only want to talk to you.
MIRI: No, don't. Don't hurt.
KIRK: Come on.
MIRI: Don't, please.
KIRK: I won't hurt you.
MIRI: Don't hurt me.
KIRK: Come on. It's all right. Come on.
RAND: We won't hurt you, sweetheart. We're your friends. No, shh!
KIRK: Take the guards, have a look outside. Radioactive readings, chemical pollutions, any further sign of life.
SPOCK: Right, Captain.
MCCOY: I wonder what happened to her, that she should be so terrified of us.
(Someone clears a patch of grime from a window, Spock goes over and peers in)
MIRI: But I remember the things you Grups did, burning, yelling, hurting people.
KIRK: We didn't do anything like that.
MIRI: You're not going to hurt?
KIRK: Well, of course not. We're here to help.
MIRI: Grups don't help.
RAND: But we will.
KIRK: What happened here? Where is everybody?
MIRI: You know.
KIRK: No, I don't. Won't you tell me?
MIRI: You got a foolie, is that it, and you want me to play, but I can't. I don't know the rules. I've got to know the rules.
MCCOY: Foolie?
MIRI: A game, you know. You can't play a game without rules. Even Grups ought to know that.
KIRK: What are Grups?
MIRI: You are. They will, when Onlies get old.
RAND: Grownups.
KIRK: You said something about the Grups doing bad things, yelling, hurting, burning.
MIRI: That was when they started to get sick in the before time. We hid, then they were gone. Am I doing all right?
KIRK: You're doing fine.
MCCOY: You said the Grups got sick. Is that why there aren't any of them around?
MIRI: Yes. They died, but that was after the awful things.
MCCOY: A plague, Captain. That could explain a lot of it.
KIRK: But what about the children, the Onlies? Didn't the awful things affect them?
MIRI: Of course not. We're here, aren't we?
KIRK: More of you? How many?
MIRI: All there are.
KIRK: What's your name?
MIRI: Miri.
KIRK: Miri. A pretty name for a pretty young woman.
MIRI: Pretty?
KIRK: Very pretty.

[Alleyway]

SPOCK: Guards! Cover me.
CHILDREN [OC]: Nyah na nyah. (stones are dropped from above) Nyah na nyah. Nyah na nyah. Nyah na nyah. Nyah na nyah. Nyah na nyah. Nyah na nyah. Nyah na nyah. Nyah na nyah. Nyah na nyah!

[House]

SPOCK: Children, Captain. Lots of them. We couldn't begin to get close to them. They just seemed to scurry away, like animals. Only children.
KIRK: Miri said all the adults died.
MCCOY: That creature which attacked us was certainly no child. Perhaps it died of the disease the girl's talking about.
KIRK: There must be records somewhere and answers to some of our questions. Miri, do you know any buildings where the doctors used to work?
MIRI: Yes, I know that. Them and their pills and things.
KIRK: Will you take me there?
MIRI: That's a bad place.
KIRK: It's important. Please.
MIRI: All right. Do you have a name, too?
KIRK: Yes. It's Jim.
MIRI: I like that name.
KIRK: Good. I like yours, too. I like you.
MIRI: Do you really?
KIRK: I wouldn't lie to you.
MIRI: I wouldn't lie to you, either, Jim. I remember the Grups, but you're nice. You're different.
KIRK: Why, thank you. (sees a mark on his hand)
MIRI: It's already starting. I knew it would. Just like it did with the Grups. It'll spread all over you, and you'll yell, and you'll try to hurt everybody and then you'll die. I knew it would! I knew it would!

Captain's Log, stardate 2713.6. The building Miri led us to also housed an automatic transmission station, which sent out the signal that drew us to this planet. We also discovered something else. That the blues blotches, characteristic of the unknown disease had appeared on each of us, with the exception of Mister Spock. There was a well-equipped laboratory in the building. Doctor McCoy took tissue samples of each of us in an attempt to isolate the organism responsible.

[Laboratory]

MCCOY: A veritable zoo of bacteria. Beam down a biocomputer and a portable electronic microscope. If I'm dealing with viruses, I'll need better equipment than I have here.

[Bridge]

FARRELL: Yes, Doctor.

[Laboratory]

FARRELL [OC]: Captain Kirk?
KIRK: Yes, Lieutenant?

[Bridge]

FARRELL: I've got volunteers standing by ready to help you, sir.

[Laboratory]

KIRK: Under no circumstances do I want anyone to beam down from the ship. We can't take any chances with further contamination.
FARRELL [OC]: But Captain, if you become too ill to
KIRK: My orders still stand, Lieutenant. You can help us best by clearing the computer banks and standing by. Kirk out. Bones, why do you think the symptoms haven't appeared in Mister Spock?
MCCOY: I don't know. Probably the little bugs or whatever they are have no appetite for green blood.
SPOCK: Being a red-blooded human obviously has its disadvantages. Now there you have a museum piece, Doctor. (referring to microscope) Lens type, manually operated, light-activated.
MCCOY: Spare me the analysis, Mister Spock, please. It is enough that it works.
MIRI: It spreads real fast. I know. When you're old, it covers you like anything.
KIRK: (reading) Intermediate experimentation report project on life prolongation.
SPOCK: Progress report, genetics section, Life Prolongation Project.
RAND: So that's what it was.
MCCOY: Life prolongation. Didn't have much luck, did they?

Captain's Log. Doctor McCoy's biocomputer and a portable electronic microscope have been beamed down from the Enterprise. They will be used in conjunction with computer banks on-board ship.

[Laboratory]

MCCOY: Tubular with extreme multiplicability. Appear to have affinity for nucleic acids. Give me what you have.
SPOCK: This was three hundred years ago, Captain.
KIRK: All the adults are dead. Only the children are left alive.
SPOCK: But children become adults.
KIRK: At least they have up to now.
SPOCK: Doctor, there are certain glandular changes which take place upon entering puberty, are there not?
MCCOY: Of course. It changes the entire body system. You know that. Of course you know that. Why?
SPOCK: Is it not possible that these children here, as they enter puberty, contract the disease?
KIRK: That would explain why there are no adults.
MCCOY: Glandular, post-pubescent. Could be.
SPOCK: It's illogical. It does not follow. All the adults on this planet died three hundred years ago, but there are children in the streets.
KIRK: Who die when they enter adolescence.
MCCOY: But how do they keep the line going?
RAND: One thing, Captain. If she were a wild animal ever since she's been a little girl, how do you explain that she wants to stay with us?
KIRK: Loneliness? I don't know, curiosity? I think children have an instinctive need for adults. They want to be told right and wrong.
SPOCK: There may be other emotions at work in this case, Captain.
MCCOY: She likes you, Jim.
SPOCK: She's becoming a woman.

[Bridge]

FARRELL: Mister Spock.

[Laboratory]

SPOCK: Spock here.
FARRELL [OC]: Here are those figures you asked for. Twelve to the tenth power. Metabolic rate seventy two percent. Production of nucleic acids reduced to thirty three percent of normal. Conventional chronological progression one hundred by three point six.
SPOCK: Acknowledged, Lieutenant. I have their calculations now.
KIRK: (to redshirts) Try again. See if you can find anything outside. (to Miri) Hey, clean up that desk for me, will you?
MIRI: All right, Jim.
KIRK: Thank you.
SPOCK: According to their life prolongation plan, what they thought they were accomplishing, a person would age only one month for every one hundred years of real time.
RAND: One hundred years and only one month?
SPOCK: Exactly, Yeoman. Evidently through some miscalculation, this virus annihilated the entire adult population in a very short period, leaving only the children.
RAND: But that means these children
SPOCK: Could very well be immensely old.
KIRK: That would certainly answer the question of what happened to their parents.
MCCOY: Answers it very well.
RAND: Children who never age. Eternal childhood, filled with play, no responsibilities. It's almost like a dream.
KIRK: I wouldn't examine that dream too closely, Yeoman. It might not turn out to be very pretty.
MCCOY: A few days ago or a week ago that creature that attacked us could have been just like Miri. A child entering puberty on this planet means a death sentence.
RAND: Do you suppose she knows?
KIRK: I don't think so.
RAND: If they're as old as Spock claims, they must have some idea of what's happening.
KIRK: There's no adult interpretation. I think we're dealing with children. Immensely old perhaps, but nonetheless children. We've got to do something about the others.
SPOCK: Difficult, if we can't even get a glimpse of them.
KIRK: You couldn't get close to the other kids?
SPOCK: Impossible. They know the area too well, like mice.
KIRK: I'm going to try. Miri? Come here. You want to go someplace with me?
MIRI: Sure. (leave, holding hands)
RAND: That little girl
SPOCK: Is at least three hundred years older than you are, Yeoman. Think about it.

[Old Toy Shop]

JAHN: Miri is with them! Why? Why? 
RED HEAD BOY: What's she going to do, Jahn?
JAHN: I don't, I don't know. I know what we've got to do. There are more of them than we see. Somewhere, up in the sky, maybe, somewhere. They talk to each other all the time. You know Grups. You know what they do, the hurting, the killing.
RED HEAD BOY: I remember, Jahn, the way it was.
JAHN: That's right, the way it was in the before time. They talk to the other Grups with these little boxes. Now, if they didn't have those little boxes, they'd be all alone, huh?
RED HEAD BOY: But they don't see us. We hide. Olly olly oxen free!
CHILDREN: Olly olly oxen free! Olly olly oxen free! Olly olly oxen free!
JAHN: No! It's not a game, it's real. They're dangerous, they're Grups. Don't you understand?
MASKED BOY: Jahn!
JAHN: (sees Kirk and Miri approach the building) All right, let's hide!
(Kirk and Miri come in, then a changing girl appears. The children flee, screaming. The girl jumps Kirk, and he eventually stuns her)
KIRK: Dead. I don't understand it. My phaser wasn't set to kill.
MIRI: Her name was Louise. She was just a little bit older than I am when it happened. Oh, Jim. (she hugs him)

[Laboratory]

FARRELL [OC]: Data has been fed into the computers, Mister Spock. Stand by.
SPOCK: Acknowledged.
MIRI: (sharpening pencils) Are these enough, Jim?
KIRK: We could use some more, if you don't mind.
MIRI: No, I don't mind.
KIRK: There couldn't be any doubt about what you found here?
SPOCK: This fellow made these notes in the last weeks after the disaster began. I disregard these last entries. He said himself he was too sick, too far gone to be sure he wasn't already mad, and I agree, but based on the entries he made before that, I know how much time we have. The ship's computers will verify my figures.
MCCOY: Only a matter of time before we all go mad, destroy each other, till the last of us finally destroys himself.
KIRK: What about Miri?
SPOCK: Our guess was correct. They contract the disease as they enter puberty and their metabolism changes. The notes would indicate it doesn't become acute for a month or so. I estimate she has perhaps five or six weeks left.
MCCOY: What about us?
SPOCK: The older the victim, the more rapid the progress of the disease.
KIRK: And you? The disease doesn't seem to be interested in you.
SPOCK: I am a carrier. Whatever happens, I can't go back to the ship, and I do want to go back to the ship, Captain.
KIRK: Of course, Mister Spock. We still don't know what we're fighting.
MCCOY: No, but we know what it is and how fast it does it. It's progressing. We'll begin to feel it inside soon. Intense fever, great pain in the extremities, fuzziness of vision. Of course, those are the early symptoms. There'll be more.
KIRK: Are You certain about the time we have left?
SPOCK: I presume my calculations are correct.
KIRK: Is there any possibility
FARRELL [OC]: Landing party, this is the Enterprise.
SPOCK: Spock here.
FARRELL [OC]: Computer indicates one hundred seventy hours, Mister Spock.
SPOCK: Verified, Captain. We have seven days.

Captain's Log, supplement. This is the second day of the seven left to us. We've found nothing. Enterprise is standing by with labs and computers ready to assist us.

[Laboratory]

KIRK: There's no data, no starting point.
MCCOY: I think I've found it.
KIRK: Janice, take Miri for a walk.
RAND: Yes, sir.
MCCOY: Only one half intact.
KIRK: But do you know what they were up to?
MCCOY: More or less. The idea was to create a new series of diseases, a chain reaction of viruses meant essentially to extend the life of the human cell immeasurably.
SPOCK: Unfortunately, they weren't successful. We've seen the results.
KIRK: You two will have to recreate their thinking. If you can isolate that virus, we'll be able to develop a vaccine.
MCCOY: Is that all, Captain? We have five days, you know.
KIRK: I know.
CHILDREN [OC]: Nyah na nyah. Nyah na nyah.
KIRK: The children! (all dash out, while Jahn sneaks in and collects the communicators from the desks)

[Corridor outside Laboratory]

KIRK: Anything?
SPOCK: No, nothing.
KIRK: And you? (clunk as grate closes)

[Laboratory]

SPOCK: Communicators, Captain, they're gone.
MCCOY: Jim, We've absolutely got to have those communicators. Without them, we don't have the computers, and without the computers, we don't have a chance.

Captain's Log, stardate 2717.3. Three days, seven hours left to us. Investigation proves that the supply of food in the area is running dangerously low. Unless something is done, the children will starve in a few months. The disease is working on each of us according to Doctor McCoy's prediction. Our tempers are growing short, and We're no further along than we were two days ago.

[Laboratory]

KIRK: Haven't you found a thing yet?
MCCOY: Would you like to take a crack at it?
RAND: (as Kirk pushes past and makes her drop flasks) No! No! No! (runs out, Kirk follows, then Miri)

[Corridor]

RAND: I'm upset, so upset. Back on the ship, I used to try to get you to look at my legs. Captain, look at my legs. (covered in blotches)
KIRK: (holds her) We're all frightened. (Miri leaves)
MCCOY [OC]: Jim, I found something!

[Laboratory]

MCCOY: The last slide I examined, I failed to make the necessary adjustment. The slowing down of my own responses
KIRK: Never mind that, what did you find?
MCCOY: The disease, Captain, the one they created three hundred years ago.
RAND: There's a chance!
MCCOY: A chance. At least it's a race now, and we've just wasted a minute.

[Old Toy shop]

JAHN: That would be some foolie, Miri, but do you think it would work?
MIRI: I know. I know. Don't you think I've heard them talk? They have such little time to do this dumb thing of theirs, this baninski thing. If we get her away. that Yeoman, that's one person less to start off with.
MASKED BOY: But how, Miri? If they're so busy, if they're going to have the big emergency, how are you going to get her away?
MIRI: It's easy. She's always asking me about the youngest little Onlies, little ones. What if they get sick, who takes care of them? Do they have enough to eat? Where do they sleep? I'll just tell her one of you fell down and got hurt.
RED HEAD BOY: Me. Say it's me.
MIRI: All right, you.
JAHN: But Grups, they know things and all that. You know, I bet they'll be able to do it with one person less.
MIRI: Not one, two. Because he'll try to find her.
RED HEAD BOY: Who? Who will, Miri?
MIRI: The Captain. He'll try to find her, but he won't. Mister Lovey-dovey.
RED HEAD BOY: Lovey-dovey. Bonk bonk on the head. Bonk bonk! bonk bonk!
CHILDREN: Bonk bonk! Bonk bonk!

[Laboratory]

MCCOY: It looks right.
SPOCK: The nitrogen cycle, it has to be.
MCCOY: But the question is, what's the dosage?
SPOCK: That is a very good question.
KIRK: Where is she, Miri? Where is she, Miri? Where's Janice?
MIRI: What's the matter with you? How should I know?
KIRK: Where is she? Has something happened to her?
MIRI: Don't you feel all right?
KIRK: No, I don't feel all right! None of us feel all right! Can't you see what's going on?
MIRI: Jim, I don't want anything to happen to you.
KIRK: I've got to find Janice.
SPOCK: That's not all, Captain. We've got to find those communicators.
KIRK: We're trying, Mister Spock. We're trying very hard.
MCCOY: That's not good enough! This could be it, but we can't test it without the ship's computers.
SPOCK: We've got to have those communicators, Jim.
KIRK: This is the vaccine?
MCCOY: That's what the computers will tell us.
SPOCK: Without them, it could be a beaker full of death.
KIRK: Did you hear them? We only have a few hours left.
MIRI: I don't care.
KIRK: You've got to care. Miri, I'm going to tell you something. You, your friends, all the Onlies are going to get the disease unless we succeed in what we're doing. You've seen your friends get it.
MIRI: Sometimes it happens.
KIRK: Not sometimes. All the times, Miri! As soon as you start growing up the way you are. Don't you know why you don't like to play games anymore, why you don't see your friends the way you used to? It's because you're becoming a young woman, and the moment you become a young woman, you get the disease. All of you.
MIRI: That's not true. It just happens sometimes.
KIRK: All the time, Miri! It's happening to you right now! Look at it. Look at it, Miri, it's in you!
MIRI: No! No! No!

[Schoolroom]

RED HEAD BOY: Blah, blah, blah!
JAHN: No, you got the wrong game. A teacher, I told you. Now, what does a teacher say, huh?
RED HEAD BOY: Yeah. Study, study, study, or bonk bonk, bad kid. (children all applaud)
RAND: It's not funny.
JAHN: It's a foolie.
RAND: What are you going to do with me?
JAHN: You think I'd tell you? Miri, you're not supposed to be here.
MIRI: I know.
JAHN: What's the matter, something go wrong?
MIRI: No.
JAHN: Okay, then. Don't just stand there in the doorway, come on in.
MIRI: Listen to him.
JAHN: You listen, Miri.
MIRI: I did. Why do you think I brought him here? Tell them, Jim.
JAHN: Tell'em, Jim. Tell'em, Jim.
CHILDREN: Tell'em, Jim! Tell'em, Jim! Tell'em, Jim! Tell'em, Jim!
KIRK: Listen to me. Listen to me!
JAHN: No yelling in the classroom! Look at him, a very bad citizen.
KIRK: This isn't a game. It never was a game.
BLONDE GIRL: Call the police!
RED HEAD BOY: I'm the police. Bonk bonk unless you're good.
JAHN: You're the teacher.
RED HEAD BOY: I got two jobs. Bonk bonk!
CHILDREN: Blah blah blah! Blah blah blah! Blah blah blah! Blah blah blah!
KIRK: Listen to me! You've got our communicators, the boxes we talk into. We need them to talk to the ship.
RED HEAD BOY: Blah blah blah!
KIRK: No blah blah blah! Because if we don't talk to the ship, if you don't help us, there won't be any games anymore. There won't be anything. Nothing, no Grups, no Onlies, nobody left forever and ever.
RAND: (sees boy with club coming up behind him) Captain.
KIRK: Now listen to me. You've got to help us before it's too late. Let Janice go. Give me those communicators before it's too late.
CHILDREN: (approaching menacingly) Nyah na nyah, nyah na nyah, nyah na nyah, nyah na nyah.
KIRK: You've seen your friends change one by one as they grew up. Did you ever see one of them not change? One by one, they got the disease, and they became like, Iike those creatures you're afraid of, like Louise. One by one they changed and got the disease. The disease like I've got, like Miri has. You understand what I'm talking about. You're not babies. We can help you!
RED HEAD BOY: Naughty Grup. (starts hitting Kirk) Bonk bonk! Bonk bonk!
MIRI: No, please. No! (the other children join in as the little blonde girl watches, smiling)
KIRK: (bleeding) It's waiting for you. It may only be a matter of months.
MIRI: Listen to him. He's telling the truth.
JAHN: He's funny. He thinks he's funny.
RED HEAD BOY: Bonk bonk! Get him!
KIRK: Look at my arms! That's what's going to happen to you unless you let me help you.
RED HEAD BOY: Bonk bonk! Hit him!
KIRK: And the little ones. What's going to happen to them after you've gone, after you've turned into creatures like Louise? Oh, they'll still be here, but not for long, because the food's all gone. You've eaten it. Maybe six months left, that's all, and then nothing left to eat, nobody left to take care of them. They'll die, too.
MIRI: Look at my arm, Jahn. It's happening to me. He's telling the truth.
JAHN: They're Grups!
CHILDREN: Bonk bonk! Bonk bonk! Bonk bonk! Bonk bonk!
KIRK: All right, you want a foolie? All right. I dare you, I double-dare you. Look at the blood on my face. Now look at your hands. Blood on your hands. Now who's doing the hurting? Not the Grups, it's you hurting, yelling, maybe killing, just like the Grups you remember and creatures you're afraid of. You're acting like them, and you're going to be just like them unless you let me help you. I'm a Grup, and I want to help you. I'm begging you, let me help you or there won't be anything left at all. Please.

[Laboratory]

MCCOY: We can't wait for those communicators any longer.
SPOCK: We must. The vaccine could be fatal.
MCCOY: The disease certainly is. How long do we have left? Hours, minutes? How much longer do you want to wait?
SPOCK: Bickering is pointless. I'll check on the Captain's progress.
(Spock leaves. McCoy picks up the hypospray and injects himself, then collapses in agony)
MCCOY: Spock!
GALLOWAY: Is he dead, Mister Spock?
SPOCK: Not yet.
KIRK: (with children and communicators) Three hours, eleven minutes left. Thank you, Lieutenant. Keep this channel open. Clear your computers. What happened to him?
SPOCK: He injected himself with the vaccine. He was unconscious when I found him.
KIRK: Look at his face.
SPOCK: The blemishes are fading. They're fading. Who will understand the medical mind?
JAHN: Is this supposed to be a good thing, Miri?
MIRI: Of course it is.

[Bridge]

RAND: They were just children. Simply to leave them there with a medical team
KIRK: Just children, three hundred years old and more. I've already contacted Space Central. They'll send teachers, advisers.
MCCOY: And truant officers, I presume.
KIRK: They'll be all right.
RAND: Miri. She really loved you, you know.
KIRK: Yes. I never get involved with older women, Yeoman. Mister Spock?
SPOCK: Captain?
KIRK: Full ahead. Warp factor one.
SPOCK: Warp factor one, Captain.