The next doctor: Christmas 1851, and Cybermen stalk Victorian London. The Doctor discovers a spate of mysterious deaths, and he's surprised to meet another Doctor. The two Doctors will need to be enough to stop the rise of the CyberKing. Planet of the dead: When a London bus takes a detour to an alien world, the Doctor must join forces with the extraordinary Lady Christina. But the mysterious planet holds terrifying secrets and time is running out as the deadly Swarm gets closer. The waters of Mars: Mars, 2059. Bowie Base One. Last recorded message: "Don't drink the water. Don't even touch it. Not one drop." The end of time: Christmas Eve, and the Doctor is reunited with Wilf to face the return of an old enemy. The Doctor faces the end of his life as the master's victory unleashes the greatest terror of all. Leads into series 5, and the Eleventh Doctor.