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 is soon called into action when people and meteorites start going missing. Most puzzling of all is the attempted kidnap of a strange hospital patient - a man with two hearts, who insists that he recognises 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.
Irregular things are happening at a nearby plastics factory, while faceless creatures lurk in the woods. The Nestenes have arrived, and want to conquer the Earth.
This story was first broadcast in the UK on BBC1 between January 3 and January 24, 1970.