Parts: 6
Writer: Terry Nation
Airdates: 8 March 1975 - 12 April 1975
Production Code: 4E

Doctor: fourth
Companions: Sarah, Harry

Megalomaniac of the Week: Davros
Creature Feature: Daleks
Special Guests: the Time Lords

Story: Instead of arriving back on the Ark, the Doctor is confused to find himself on the surface of a rocky, misty planet where the sounds of war are present all around. A Time Lord appears before the Doctor and tells him that they have a request for him: they want him to travel back in time to Skaro, before the Daleks' creation. If he cannot destroy them before they begin, or alter their genetics so that they evolve into less aggressive creatures, he may learn some inherent weakness that can be used to defeat them in the future.

The Doctor eventually agrees to one last mission from the Time Lords, at which point he learns that he is already on Skaro. The Time Lord vanishes, and the Doctor is rejoined by Sarah and Harry. As the TARDIS crew make their way across the landscape of war-torn Skaro, they learn that it is far from the safest place to be: landmines litter the ground, bombs explode all around, corpses are used to man trenches, and clouds of gas threaten to suffocate them. When they are eventually attacked, Sarah is left for dead while the Doctor and Harry are taken prisoner by the Kaleds.

Very quickly, the TARDIS crew are embroiled in a vicious and horrific war in which both the Kaleds and the Thals are determined to eradicate the other side. But there is a third factor that neither had anticipated: the Kaleds' most revered scientist, Davros, who will go to any lengths to ensure that his new creations - the Daleks - survive. Mutated creatures lurk in the shadowy corners, Davros' agents are on the prowl, and no-one knows who can be trusted. Can the Doctor and his companions survive long enough to end the Dalek menace once and for all?