"The Snowmen" - Official Synopsis

Following the release of the stunning images last night (which you can find here), the BBC have released the synopsis for "The Snowmen":

Christmas Eve 1892 and the falling snow is the stuff of fairy-tales. When the fairy-tale becomes a nightmare and a chilling menace threatens Earth, an unorthodox young governess, Clara, calls on the Doctor for help. But the Doctor is in mourning, reclusive and determined not to engage in the problems of the universe. As old friends return, will the Doctor really abandon humankind or will he fight to save the world – and Christmas – from the icy clutches of this mysterious menace.