While the Dalek inventor Zeg is working in the inventions factory on strengthening Dalekanium, a fierce storm hits the Dalek city and a lightning strike damages Zeg's equipment. The ensuing explosion coats Zeg in the newly created metal. A team of Daleks brings Zeg to the examination chamber, where they find his casing stronger, but are concerned by his claims of invincibility. They fire at him but can't destroy him.
In the City Centre, the Dalek Emperor speaks about the problems of metal fatigue slowing the space conquest programme when Zeg announces that his metalert is the key. He demands they make him the new Emperor on the basis of his greater strength. The Black Dalek is summoned to test Zeg's claim but even his gunstick can't destroy him. The Emperor puts the matter to the Brain Machine, but popular support is already moving to Zeg. The Brain Machine declares that Zeg must prove his intelligence and the Emperor must prove his strength in a duel for leadership.
The next day Zeg searches for the Emperor on the plain where they were to meet. When he reaches the acid river, the Emperor blasts away at the rock ledge beneath him. Zeg escapes the acid river unscathed and follows the Emperor's trail to the mercury geysers, where he fires on his rival, who proves to be an inflatable facsimile. The Emperor has used the ruse to get Zeg within range of a geyser diverted towards him.
Unaffected by the mercury, Zeg pursues the Emperor into the abandoned Dalek workshops. When the Emperor douses Zeg in liquid oxygen from one of the tanks, the cold cuts through him and he explodes. The Emperor promises the other Daleks that they will improve on Zeg's invention and take to the stars.
- vep, a unit of artificial sunlight. Twenty veps is described as incredible heat, eighty is blistering.
- meg, a unit of time likely equal to one second, (see rel)
to be added
- reprinted in black-and-white in Doctor Who Weekly issues 35-36
- reprinted in colour in Doctor Who Magazine issues 189-193
- reprinted in colour in DWMS The Dalek Chronicles
- Magnetised sand was used in the last story to conceal the city. Here it is used as defence against the elements.
- The Daleks began working on space-flight after recovering the plans to the Krattorian vessel.
- Even before Zeg's challenge, the Emperor had been tested by the Brain Machine to validate his claim. This does not contradict Genesis of Evil in which he just made himself Emperor.
- It is implied that the Black Dalek has a stronger weapon.