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?
A meeting in a London bus with jewel thief Lady Christina takes a turn for the worse for the Doctor when the bus takes a detour to a desert-like planet, where the deadly Swarm awaits.
The Doctor is a Time Lord: a 900 year old alien with 2 hearts, part of a gifted civilization who mastered time travel. The Doctor saves planets for a living—more of a hobby actually, and the Doctor's very, very good at it.
