Doctor Who Season 4 Episode 13

Martha: I've got the Osterhagen Key. Leave this planet and its people alone or I'll use it.
The Doctor: Osterhagen what? What's an Osterhagen Key?
Martha: There's a chain of twenty-five nuclear warheads placed in strategic points beneath the Earth's crust. If I use the Key, they detonate and… the Earth gets ripped apart.
The Doctor: WHAT? Who invented that? (as an aside, to himself, aloud) Well, someone called Osterhagen, I suppose. Martha, are you insane?
Martha: The Osterhagen Key is to be used if the suffering of the human race is so great, so without hope, that this becomes the final option.
The Doctor: That's never an option!
Martha: Don't argue with me, Doctor, 'cause there's more than that. Now, I reckon the Daleks need these twenty-seven planets for something, but what if it becomes twenty-six? What happens then? Daleks, would you risk it?
Rose: Oh, she's good.
Martha: Who's that?
Rose: My name's Rose. Rose Tyler.
Martha: Oh my God. He found you.