John Woodnutt

The Doctor, Sarah and Harry return to Earth to help the Brigadier discover what is causing the destruction of oil rigs off the coast of Scotland.

Sarah is attacked by a Zygon disguised as Harry who is a prisoner on the Zygon spaceship. The Doctor falls into a trap and is hunted down by the giant Skarasen.

The Doctor and Sarah find their way into the Zygon spaceship at the bottom of Loch Ness while the Brigadier prepares to force it to the surface with depth charges.

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 colonizing the Earth.

The Zygon warlord, Broton, disguised as the Duke of Forgill, intends to use the Skarasen to attack the World Energy Conference in London.