As the newly-regenerated Doctor arrives on Earth, so does the Nestene too.

UNIT's attempts to locate the meteorites are hampered by the mysterious plastic Autons, being constructed by Channing at a nearby factory, while the Doctor makes another attempt to escape from the hospital.

Ransome manages to escape from the plastics factory and alert UNIT, prompting the Doctor and the Brigadier to start an investigation.

With UNIT's investigation being blocked by the Replica of Scobie, the Doctor and Liz visit Madame Tussaud's to try and find out more as Channing prepares to activate the Autons.

The English channel, the 1900s AD. The TARDIS lands on barren Fang Rock, inhabited until now only by three lighthouse keepers. But what is the strange fog covering the island, and can it be connected to the falling star sighted earlier that night?

The survivors of a wrecked ship are stranded with the lighhouse crew on Fang Rock as a deadly menace slithers through the fog. Has the Beast of Fang Rock returned?

The Doctor barricades everyone in the lighthouse to protect them from the mysterious deadly creature in the fog. But it may already be inside, biding its time…

The Rutan starts picking off the surviving humans one by one as the Doctor and Leela struggle to defeat not only the alien but an entire fleet waiting to occupy Earth.