Parts: 4
Writer: Robert Holmes
Airdates: 2 September 1978 - 23 September 1978
Production Code: 5A

Doctor: fourth
Companion: the first Romana, K-9 mark two

Creature Feature: Shrievenzale

Story: The Doctor's plans for a holiday with K-9 are dashed when the TARDIS is waylaid by the White Guardian. As the Guardian is one of the most powerful beings in the Universe, the Doctor dare not decline when he is offered a great task. The chaotic forces in the Universe are growing, the Guardian tells him, and becoming more threatening - and in order to restore the balance, the Guardian needs the Key to Time. A powerful tool able to halt the entire cosmos, the Key was divided into six segments which were scattered throughout the universe to keep them from falling into the wrong hands. Because they can be disguised as any object, the Doctor is given a tracer - and a new assistant, Lady Romanadvoratrelundar.

The Doctor and Romana trace the first segment to the primitive planet of Ribos, currently in its Ice Time - one of two long seasons - and thus bitterly cold. They quickly locate the segment amongst the planet's crown jewels, but before they can obtain it, Romana is attacked by a fierce monster. Meanwhile, con-men Garron and Unstoffe are attempting to sell the planet under false pretences.

The Graff Vynda-K, target of Garron's plans, is completely taken in by Garron's reports that Ribos contains high levels of the valuable stone jethryk - until he discovers evidence that Garron is not as honest as he has tried to appear. Once this treachery has been confirmed, the furious Graff intends to execute him...along with his accomplices, the Doctor and Romana. The Doctor's quest for the Key may end before it even starts...