They've also said they are going to get it made as quickly as possible. http://www.digitalspy.co.uk/tv/s129...make-it-as-quickly-as-we-can-says-moffat.html
They are already trying to sort out schedules and dates. It's gotta happen just a question of how soon.
Anyway I've read a couple of reviews and here is what is said, it pretty much shoves in your face that (A COUPLE OF BIG POTENTIAL SPOILERS)Mary is someone who we do not expect, one review in particular seems to say that she is a full on threat. They never mention Mary but say it's a big character. And seeing as there aren't many other options it has to be her.
They also say there are MANY clues to this reveal in the last two episodes and that after Vow you will view this episodes a little differently.
There's also another surprise cameo (this show being of little cast means it can really only be Adler or Moriarty)
It also ends on a BIG cliffhanger. Again.
Apparently the twist character has had a lot of hints toward their twist in the other two episodes. I see that with Mary. Not Molly. Though Molly would be cool
I can think of one hint for each, liar with Mary and Molly looking nervous after the CAM telegram, anyone know the others?
Absolutely brilliant last episode of the series.
Guess who's back?
Moriarty.
t:Absolutely brilliant last episode of the series.
Guess who's back?
Moriarty.

Even the Grand Moff said that he could come back he just needed a break after being the main villain two series running.
absolutely brilliant last episode of the series.
guess who's back?
moriarty.
And people say the Moff never lies.
I don't think he is directly back. I think he is very much dead and has something planned from beyond the grave.