The BBC have released the official synopsis for A Christmas Carol:

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?

Amy Pond is played by Karen Gillan, Rory Williams by Arthur Darvill, The Doctor by Matt Smith and Kazran Sardick by Michael Gambon.

A Christmas Carol airs on BBC One and BBC HD on Christmas Day.