[Planet surface]

(The landing party is Kirk, Spock, Scott, Uhura and two security guards. Among remains of fluted columns and fragments of Greek-style buildings is a blue police box with a light on top.)

KIRK: These ruins extend to the horizon. Begin recording. UHURA: Recording, sir. SPOCK: And of considerable age. On the order of ten thousand centuries old. KIRK: Detail, fan out. What is this thing, Mister Spock? It seems to be pulsating with power of some kind. Analysis, please. SPOCK: Unbelievable, Captain. KIRK: That's funny. SPOCK: This single object is the source of all the time displacement. KIRK: Explain. SPOCK: I can't. For this to do what it does is impossible by any science I understand. It is operating even now. Putting out waves and waves of time displacement, which we picked up millions of miles away. UHURA: Landing party to Enterprise. No sign of Doctor McCoy. Search progressing. (And he pops up from behind a rock after she and her security guard have passed by.) SPOCK: Incredible power. It can't be a machine as we understand mechanics. KIRK: Then what is it? TARDIS: (The light pulses bright with the words) A question. Since before your sun burned hot in space and before your race was born, I have awaited a question. KIRK: What are you? TARDIS: I am the Tardis of Forever. KIRK: Are you machine or being? TARDIS: I am both and neither. I am my own beginning, my own ending. SPOCK: I see no reason for answers to be couched in riddles. TARDIS: I answer as simply as your level of understanding makes possible. SPOCK: A time portal, Captain. A gateway to other times and dimensions, if I'm correct. TARDIS: As correct as possible for you. Your science knowledge is obviously primitive. SPOCK: Really. KIRK: Annoyed, Spock? TARDIS: Behold. A gateway to your own past, if you wish. (A camel train passing a pyramid, ancient Rome - images appear in holographic display.) MCCOY: Killers! Killers! I won't let you get me! I'll kill you first! I won't let you get me! Assassins! Murderers! Killers! (Scott and a guard manage to grab McCoy, and Spock neck-pinches him.) KIRK: Spock! If that is a doorway back through time, could we somehow take Bones back a day in time, then SPOCK: Relive the accident. This time be certain that the hypo accident is avoided. Look at the speed with which the centuries are passing, Captain. To step through on precisely the day we wish KIRK: Tardis. Can you change the speed at which yesterday passes? TARDIS: I was made to offer the past in this manner. I cannot change. (The US cavalry charges.) KIRK: Strangely compelling, isn't it? To step through there and lose oneself in another world. SPOCK: I am a fool. My tricorder is capable of recording even at this speed. I've missed taping centuries of living history which no man before has ever (But McCoy has woken up, and dashes towards the Tardis.) SCOTT: Doctor McCoy! KIRK: Bones, no! (McCoy leaps through the doors and a whirring sound begins as the blue box dematerializes. He's gone.)