Parts: 6
Writer: Malcolm Hulke
Airdates: 10 April 1971 - 15 May 1971
Production Code: HHH
Megalomaniacs of the Week: the Master, IMC
Creature Feature: Primitives
Special Guests: UNIT (the Brigadier)
Story: The Doctor's attempts to fix the dematerialization circuit seem to have finally succeeded, when the TARDIS takes off while he and Jo are inside. But the Doctor soon finds that his craft is being operated by remote control - that of the Time Lords. They send him to the planet Uxarieus...but for what purpose?
On Uxarieus, a fledgling colony from Earth is trying to establish a hold on the planet, but difficulties abound. Their crops are failing for no apparent reason, a mining corporation is trying to force them off the planet, and giant lizards have appeared from nowhere to attack the colonists - so even if they can avoid being sent back to Earth, they will probably either starve to death or be decimated by lizard attacks.
The Doctor and Jo soon become embroiled in the conflict between the colonists and the Interplanetary Mining Corporation, whose unscrupulous methods make them a formidable opponent indeed. But there is another faction on the planet - the green-skinned primitive natives, who have been guardedly helping the colonists...but can they be trusted? And what role will the Adjudicator from Earth play? As the stakes get higher, and the lives of the colonists hang in the balance, the Doctor and Jo must work to establish peace between the various factions...but their efforts are being undermined from the inside...