Forbidden to continue his travels through time and space by his fellow Time Lords, the newly regenerated Doctor (Jon Pertwee) begins his exile on 20th century Earth. His arrival coincides with a shower of strange meteorites, which are promptly investigated by the United Nations Intelligence Taskforce. Although his old friend Brigadier Alastair Gordon Lethbridge-Stewart (Nicholas Courtney) is initially suspicious of the Doctor's new appearance and personality, he is forced to ask for his help when several of the meteorites go missing. The Doctor discovers that the meteor shower was in fact the first wave of an invasion by hostile alien intelligence the Nestene; phase two begins when the Autons - deadly plastic mannequins created by the Nestene agents on Earth - launch an attack on the unsuspecting public.