"Imagine that you can live forever and life is totally free from pain. You can see all things with clarity, unblinkered by irrelevant details. You will never fear, never sicken, never lose control. That is what the Cybermen are offering."

The Doctor takes his new companion, Grant, back home to Agora — only to find a world in the thrall of some of his oldest and deadliest foes.

The Cybermen have taken control and set up a breeding colony to propagate their own race. While the Doctor languishes in a cell at the mercy of the sadistic Overseers, Grant joins up with a group of rebels and works on a desperate rescue bid.

With time running out, the rebels move into action. But will their solution prove more deadly than the problem itself?