The Dominators — Ian Marter

The Doctor remembers Dulkis from a previous visit as a civilized and peaceful place. But times have changed, and his second trip is not quite the holiday he was expecting.

The Dulcians themselves are more reluctant than ever before to engage in acts of violence. The so-called Island of Death, once used as an atomic test site, had served as a dire warning to generations of Dulcians of the horrifying consequences of warfare. But an alien race prepares to take advantage of their pacifism.

The whole planet and its passive inhabitants are threatened with complete annihilation--and no one, it seems, is going to life a finger to stop the evil Dominators and their unquestioning robot slaves.