A mysterious plague strikes Space Beacon Nerva, killing its victims within minutes. When Doctor Who lands, only four humans remain alive. One of these seems to be in league with the nearby planet of gold, Voga... Or is he, in fact, working for the dreaded Cyberman, who is now determined to destroy their old enemies, the Vogans?

The Doctor, Sarah, and Harry find themselves trapped in the midst of a terrifying struggle to death - between the ruthless power-hungry Cybermen and the determined, desperate Vogans.