Alright, since we appear to be done with the white text....
You beat me to it! I was thinking the same thing after watching the episode - technically the Master had to get there somehow, so his TARDIS must be there. The issues are:
- what state is it in? Just as the Doctor could sense other Timelords (or the lack thereof) would the TARDIS itself (or at least equipment onboard the TARDIS) not be able to sense other TARDISes as well, being that they are technically living entities? How come the Doctor wasn't made aware of it in this case? So, is it dead, badly damaged, or just lying dormant?
- even if it is there somewhere, how do they find it? Assuming the Master's TARDIS's chameleon circuit is actually functioning as it should, they aren't exactly going to be looking for another blue police box!
And yes, there's always Jack's device as well... I guess we'll see...
The other thing I thought of is that the Master rgenerated inside the TARDIS without the Doctor seeing him. Perhaps the Doctor realized he regenerated, yes, however he no longer know what he looks like. So, even if they do track him down (which obviously they do!) the Doctor will not know what the Master looks like and that he is indeed Mr. Saxon!

Sure, he can sense that the Master is alive now, but I doubt his senses are good enough to discern exactly who and when he is...

So, this will be another hurdle for the Doctor - as if escaping from the end of the universe isn't enough already!
