DOCTOR: I could take you forward -

SAM: No. We've figured it out. I'm going to be staying here. Sarah's got a couple of big projects lined up in the next year or so. She's going to need help. And there's a spare room here, so I won't get in the way of... you know. Her private life.

SARAH: I'm hoping there'll be a Nobel Prize in this somewhere.

SAM: Either that or we'll end up bringing down Western civilisation.