The colony planet Delafoss is occupied by the army of a rapacious alien force known only as the Eminence. These slave armies of terrified humans are commanded by the dreaded Infinite Warriors - impervious to most forms of firepower, voices like icy death. The Doctor and Leela arrive expecting to find Earth's most successful, unspoiled colony. Instead, they are confronted by a planet choked by industrialization. And at the heart of it all, the construction of something that the Eminence intends will wipe out all human resistance once and for all!