DOCTOR: When something goes missing, you can always recreate it by the hole it left. I know that there was an ice warrior on the submarine and a mummy on the Orient Express. I know we sat together in the cloisters and she told me something very important, but I have no idea what she said... Or what she looked like... Or how she talked... Or laughed.

CLARA: You don't know who you're looking for, I mean... She could be me, for all you know.

DOCTOR: There's one thing I know about her. Just one thing. If I met her again, I would absolutely know.