Here is the official synopsis from www.bbc.co.uk:
'Amy and Rory are trapped on a crashing space liner, and the only way The Doctor can rescue them is to save the soul of a lonely old miser, in a festive edition of the time-travelling adventure, written by Steven Moffat. But is Kazran Sardick, the richest man in Sardicktown, beyond redemption? And what is lurking in the fogs of Christmas Eve?'
Joining Matt Smith (The Doctor), Karen Gillan (Amy Pond) and Arthur Darvill (Rory Williams), Michael Gambon plays Kazran Sardick and Katherine Jenkins plays Abigail.
While I'm very excited to be able to get the Christmas Special the same day, I am a little apprehensive. The Christmas Carol story by Charles Dickens as this seems to be gleamed from, is not a favorite of mine, mostly because I feel it's been done to death. I also have some doubts about Rory and Amy being aboard a doomed space liner as this happened in "Voyage of the Damned" Just 2 years ago. However, if this last series of episodes as shown us anything, it's to have faith in Steven Moffat, he hasn't let us down yet.
Doctor Who: A Christmas Carol will air on Christmas Day at 9:00 pm on BBC America.