DOCTOR: I tolerate this century, but I don't enjoy it. Have you ever thought what it's like to be wanderers in the fourth dimension? Have you? To be exiles? Susan and I are cut off from our own planet, without friends or protection. But one day we shall get back. Yes, one day. One day.

IAN: Susan Foreman? She your problem too?

BARBARA: Yes.

IAN: You don't know what to make of her?

BARBARA: No.

IAN: How old is she, Barbara?

BARBARA: Fifteen.

IAN: Fifteen. She lets her knowledge out a bit at a time so as not to embarrass me. That's what I feel about her. She knows more science than I'll ever know. She's a genius. Is that what she's doing with history?

BARBARA: Something like that.

DOCTOR: Fear makes companions of all of us.

DOCTOR: If you could touch the alien sand and hear the cries of strange birds and watch them wheel in another sky, would that satisfy you?

DOCTOR: It's still a police box. Why hasn't it changed? Dear, dear, how very disturbing.

SUSAN: Grandfather!

SUSAN: Yes, I can see red turns to blue, Mister Chesterton, but that’s because we’re dealing with two inactive chemicals. They only act in relation to each other.

IAN: But that’s the whole point of the experiment, Susan.

SUSAN: Yes, it’s a bit obvious, isn’t it? Well, I’m not trying to be rude, but couldn’t we deal with two active chemicals? Then red could turn blue all by itself and get on with something else? I’m sorry, it was just an idea.

SUSAN: The TARDIS can go anywhere.

BARBARA: TARDIS? I don’t understand you, Susan.

SUSAN: Well, I made up the name TARDIS from the initials, Time And Relative Dimension In Space. I thought you’d both understand when you saw the different dimensions inside from those outside.

IAN: Just let me get this straight. A thing that looks like a police box, standing in a junkyard, it can move anywhere in time and space?

SUSAN: Yes.

DOCTOR: Quite so.

IAN: But that’s ridiculous.

BARBARA: Are you saying you don't know how to work this thing?

DOCTOR: Of course I can't! I'm not a miracle worker!

BARBARA: I suppose we are doing the right thing, aren't we?

IAN: You can't justify curiosity.