The Earth is in terrible danger! The Master is back with an evil scheme to destroy humanity and silence the Doctor forever. His plan? To awaken the awesome power of the Nestene – a ruthlessly aggressive alien life form. Once mixed with plastic, they will form into faceless automatons, a willing army of destruction easily controlled by the evil Time Lord himself. This is the terrible threat now facing the Earth – the terror of the Autons.
The Doctor is caught up in events at Stangmoor Prison, where Professor Keller’s new machine is said to be able to remove all evil impulses from the minds of the prisoners.
An approaching Alien spaceship is detected on monitoring equipment at UNIT HQ, where the Brigadier is entertaining two visitors – Chinn, a civil servant making a security inspection, and Bill Filer, an American agent sent to discuss the threat of the Master. The Ship lands in England and the UNIT team, joined by Hardiman and Winser from the nearby Nuton power station, meet its occupants: beautiful golden-skinned humanoids called Axons.
The Time Lords discover that the Master has stolen their secret file on the Doomsday Weapon and decide to send the Doctor to retrieve it for them. The TARDIS takes the Doctor and Jo to the desolate planet Uxarieus in the year 2472. There they become involved in a dispute between some beleaguered colonists and the crew of an Interplanetary Mining Corporation (IMC) spaceship over the ownership rights to the planet. The Doctor learns that the indigenous Primitives and their High Priests worship a large machine tended by a creature called the Guardian.
In the peaceful village of Devil’s End something very strange is happening. A professor is preparing to open a nearby burial mound and a local white has foresees death and disaster. Meanwhile, the new vicar looks suspiciously like the Master and he is using black magic to conjure up an ancient Dæmon.