The Doctor: They're following us.
Martha: How can they do that? You've got a time machine.
The Doctor: Stolen technology. They've got a time agent's vortex manipulator. They can follow us wherever we go. Right across the universe. They're never going to stop. Unless… I'll have to do it. Martha, you trust me, don't you?
Martha: Of course I do.
The Doctor: Cause it all depends on you.
Martha: What does? What am I supposed to do?
The Doctor: Take this watch, cause my life depends on it.