I was watching the first season 4 trailer and I realized: that woman, the one who walks so confidently, she's using a sonic screwdriver! After I saw that, I saw the doctor had both screwdrivers in his hands and was using his on that womans.  - . ^   Using that knowledge, I hypothesis that I think that the confident woman is... The Rani!

Yes, I know, after the Master, it'll be overdone.  Plus everyone knows that... , but the first trailer is usually only the first couple episodes, because that is all they've shot and cut ( And because RTD et all said so in that audio voice over that they do ((they said so at the very end of it, go listen if you want, it's on the BBC website under downloads or video or audio or something)).  Most of the shots were from the beginning episodes.)   So it won't be part of the last episodes, but among the first.

So, (what was my point again? I've lost it...)  This might not be a big big thing like they made the Master out to be.  Now that they've already done it, it'll be like the Daleks coming back in 'Daleks in Manhattan"  and just be 2 episodes or something.

Well, it's a thought, and I'm declaring it now, so that I can prove myself superior to everyone if I'm right.   Ha.