Parts: 4
Writer: William Emms
Airdates: 11 September 1965 - 2 October 1965
Production Code: T

Episode Titles: Four Hundred Dawns; Trap of Steel; Air Lock; The Exploding Planet

Doctor: first
Companions: Vicki, Steven

Megalomaniacs of the Week: Drahvins
Creature Feature: Rills

Story: A wobbly-moving, chittering robot surprises the Doctor, Vicki and Steven by coming to examine the TARDIS soon after it has materialized. Vicki, finding it cute, decides to call it a Chumbley. After the Chumbley departs, the TARDIS crew ventures onto the planet's surface, where they are accosted by another Chumbley - this one carrying a weapon, and therefore not so cute.

The TARDIS crew are rescued from the Chumbley by two stately, and very beautiful, women - Drahvins, from the planet Drahva in Galaxy Four. As they refuse to answer any questions - instead insisting that they will take the TARDIS crew back to their leader, Maaga - Vicki is unsure that she wishes to accompany them. To allay Vicki's fears, the Drahvins inform them that if they stay, more Chumblies will come to capture them and take them to the Rills, hideous and evil creatures. Given the choice, the Doctor decides it would be prudent to go with the Drahvins.

Unfortunately, the TARDIS has brought the Doctor and his friends right into the middle of a war between the Drahvins and the Rills. To make the situation even worse, the Drahvins report that the planet they are on will explode within fourteen days. But the Doctor is suspicious that they may not have even that much time, and he is not much more inclined to believe anything else the Drahvins say. And for good reason - appearances can be very deceiving, and the Drahvins are willing to do almost anything to ensure their safe escape from the doomed planet...