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 industrialisation. 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.

For the first time in his life, the Doctor confronts the Eminence... and things will never be quite the same again.