The Sontaran Stratagem

DONNA: Doctor.

DOCTOR: Oh, just in time. Come on, come on, we're going to the country. Fresh air and geniuses, what more could you ask?

DONNA: I'm not coming with you. I've been thinking. I'm sorry. I'm going home.

DOCTOR: Really?

DONNA: I've got to.

DOCTOR: Oh, if that's what you want. I mean, it's a bit soon. I had so many places I had wanted to take you. The Fifteenth Broken Moon of the Medusa Cascade, the Lightning Skies of Cotter Palluni's World, Diamond Coral Reefs of Kataa Flo Ko. Thank you. Thank you, Donna Noble, it's been brilliant. You've, you've saved my life in so many ways. You're, (penny drops) you're just popping home for a visit, that's what you mean.

DONNA: You dumbo.

DOCTOR: And then you're coming back.

DONNA: Know what you are? A great big outer space dunce.

DOCTOR: Yeah.