TV Preview: Doctor Who – The Great Detective

Yesterday during the Children In Need live broadcast a short prequel to the Doctor Who Christmas special was shown. It looks great:

And there’s a brand new trailer:

I’m still very curious to see how Jenna-Louise Coleman will fit in to all this. She and Matt Smith are saying that she isn’t the same character, but somehow that only makes me think that she is. But how? The other guess for now is that she’s an ancestor of Oswin, but somehow that seems to be too simple an explanation. I’m hoping it’s a bit more mysterious than that. What do you think? Any theories?