The Doctor: I don't understand. Who are you?
Idris: You really don't know me? Just because they put me in here?
The Doctor: They said you were dangerous.
Idris: Not the cage, stupid. In here. (gestures to head) They put me in here. I'm the-- (beat) Oh, what do you call me? We travel. I go (makes the TARDIS materialisation noise).
The Doctor: (disbelieving) The TARDIS?
Idris: Time And Relative Dimension In Space. Yes, that's it. Names are funny. It's me, I'm the TARDIS.
The Doctor: No, you're not! You're a bitey mad lady. The TARDIS is up and downey stuff in a big blue box.
Idris: Yes, that's me: A Type 40 TARDIS. I was already a museum piece when you were young. And the first time you touched my console, you said--
The Doctor: (interrupting) I said you were the most beautiful thing I had ever known. (relisation)
Idris: Then you stole me. And I stole you.
The Doctor: (long pause) I borrowed you.
Idris: Borrowing implies the eventual intention to return the thing that was taken. What makes you think I would ever give you back?