The Doctor arrives in Victorian London. It's Christmas, but snow isn't the only thing descending on the tranquil and jubilant civilization, as familiar silver giants from an alternate reality are amassing in numbers. The Cybermen are on the move again, and the only beings who can stop them are the Doctor and... another Doctor?

In 1960s New York, Walter Stackhouse is a rich, successful architect and unhappily married to the beautiful but damaged Clara. His desire to be free of her feeds his obsession with Kimmel, a man suspected of brutally murdering his own wife. When Walter and Kimmel's lives become dangerously intertwined, a ruthless police detective becomes convinced he has found the murderer. But as the lines blur between innocence and intent, who, in fact, is the real killer?