The TARDIS brings the Doctor and Mary Shelley to the continent of Zelonia, on the frontier world Draxine — where, many moons ago, the twin citystates of Garrak and Stronghaven bore testament to mankind's colonial spirit.

That was before the sinister death cult of Garrak's President Harmon took hold — and Garrak annihilated itself, utterly, in an apocalyptic explosion. Before the bones of Garrak's dead came back to life, and its skeletal citizens began marching, marching, marching on Stronghaven itself.

But what do they want, this army of death? And can anything stop them? In search of answers, the Doctor and Mary must journey into the dead heart of a dead city to face a terrifying adversary, whose ambitions transcend the stuff of life itself.