The TARDIS arrives on Earth in the middle of a meteorite shower and the Doctor is found by UNIT troops and taken to a nearby hospital. The Brigadier is faced with having to cope not only with the mysterious meteorites but also with Ransome, an ex-employee of a local plastics factory, who claims he has seen a walking mannequin.

The meteorites turn out to be hollow globes containing the Nestene consciousness, a disembodied alien intelligence with an affinity for plastic. A Nestene agent, Channing, has infiltrated the plastics factory and is using energy from the globes to animate Autons - mannequin-like figures and realistic replicas of senior establishment figures - with the aim of colonising the Earth.

Aided by newly-recruited UNIT scientist Dr Elizabeth Shaw, the Doctor thwarts this scheme by repelling the Nestene consciousness into space and thereby neutralising the Autons and the monstrous tentacled form that it has been creating for itself in a tank within the factory. Channing, revealed to be no more than a sophisticated Auton, is likewise deactivated.