"Is that finger loaded?"The TARDIS lands in a typical English village that Sarah recognises as Devesham, home of the British Space Defence Station. However, it soon becomes obvious that things are not all as they should be, and the Doctor and Sarah realise that the village is a replica populated with androids.An alien race — the Kraals — are aided by a brainwashed human astronaut, Guy Crayford, and have built the replica to rehearse for an invasion of the Earth. Styggron, a Kraal scientist, has perfected a lethal virus and plans to use his androids to disseminate it around the world, paving the way for the Kraal fleet.Crayford, whose rocket had been damaged and who was rescued by the Kraals, returns to a hero's welcome. But with the Brigadier off in Geneva, no-one at UNIT believes the Doctor when he tells tall stories of android replicas — which now include himself, Harry and RSM Benton. The Doctor manages to use the radio equipment at the base to jam the android control signal and stop Styggron releasing the virus. He then uses his own android replica to fight Styggron, who infects himself with the virus in the process and is killed.
— The Doctor sizes up the threat.