Found guilty by his fellow Time Lords of interference in the affairs of other planets, the Doctor is forced to undergo his second regeneration and is exiled to Earth.

But strange meteorites are landing in Essex and Brigadier Lethbridge-Stewart of UNIT has reason to believe that they were deliberately aimed at the Earth’s surface. In order to avert a possible catastrophie the Doctor joins forces with UNIT and battles with the sinister Autons – creatures whose murderous behaviour is directed by the Nestene Consciousness, a hideous entity of cosmic proportions.