The Master shifts his stance a little, disturbed. Now that the Doctor has called attention to it, there is something a bit off to the feel of this world.

"You have tried to return then? And failed?"

That...is not good news. The Doctor never fails, so far as the Master can tell. Oh, he has setbacks and, occasionally, things don't quite the way he wants, but that is more others failing and the Doctor living with the consequences! If the Doctor actually can not find an answer he seeks, then the situation is dire indeed.