 Exiled to Earth in the late 20th Century by his own people, the Time Lords. The newly regenerated Doctor arrives in Oxley Woods alongside a shower of mysterious meteorites. Investigating these unusual occurrences is the newly-formed United Nations Intelligence Taskforce (UNIT) for short. Led by Brigadier Alistair Gordon Lethbridge-Stewart, UNIT are soon called into action when people and meteorites start going missing. Most puzzling of all is the attempted kidnapping of a strange hospital patient, a man with two hearts, who insists that he knows the Brigadier. The new Doctor soon joins forces with his old friend, UNIT and the recently recruited Dr Liz Shaw, but time is running out as Nestine consciousness is planning to invade Earth... (Originally broadcast in four parts.)