DOCTOR: Even after all this time he cannot understand. I dare not change the course of history. Well, at least I taught him to take some precautions. He did remember to look at the scanner before he opened the doors. Now they're all gone. All gone. None of them could understand. Not even my little Susan, or Vicki. And as for Barbara and Chatterton. Chesterton. They were all too impatient to get back to their own time. And now, Steven. Perhaps I should go home, back to my own planet. But I can't. I can't.

DOCTOR: Well, my boy, we finally rid this planet of Daleks.

STEVEN: Bret, Katarina, Sara.

DOCTOR: What a waste. What a terrible waste.

VICKI: Doctor? He says the TARDIS isn't a time machine.

DOCTOR: Oh, does he now?

VICKI: Tell him.

DOCTOR: I don't see why I should, my child. He'll learn soon enough.

STEVEN: Look, Doctor, I've seen some spaceships in my time, admittedly nothing like this. Well, what does this do?

DOCTOR: That is the dematerialising control and that, over yonder, is the horizontal hold. Up there is the scanner, those are the doors, that is a chair with a panda on it. Sheer poetry, dear boy. Now please stop bothering me.

STEVEN: Look, you gave this ship a name just now, what was it?

VICKI: TARDIS, T A R D I S. It stands for Time And Relative Dimensions In Space.

STEVEN: IDBI.

VICKI: What? IDBI?

STEVEN: I D B I.

VICKI: Yes?

STEVEN: It means I Don't Believe It.