The Snowmen (S07E06)

Christmas Eve, 1892, and the falling snow is the stuff of fairytales. When the fairytale 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? (BBC)