As well-meaning as Martha's comments were, the Doctor's expression dimmed at the final two questions. He turned away from her in a behavior that she was sure to recognize, and started fiddling with controls that didn't need to be fiddled with. It was classic pretend-everything-is-all-right avoidance, and as usual, it wasn't so much an attempt to hide what was wrong as to warn his companion away from asking about it.
"About that ... I'm sorry, Martha. I really am. You should've been sent to a different part of the sixties, with me, and we should be working out how to fix it with the help of Sally Sparrow's notes. The thing is, you've somehow gotten a bit sidetracked from your proper timeline. So have I. And I'm sorry. I'm very, very sorry, but there's nothing I can do about that right now. I can barely move to TARDIS from one part of New York to another. We're lucky she's even functioning. The last time she got pulled into an alternate dimension without warning, the core went dead."