Governor Gremla rules five confederations of planets in the galactic empire of Siemb with an iron fist. Her lieutenant Arkos has turned against her, which makes him an enemy of the empire. The hero Caberhi Tram is sent to the planet Hypsis — known as the prison planet — to track him down. Arkos has prepared for this: after attacking Gremla's palace and weakening the Imperial Palace-Planet Sckunn, he returned to Hypsis and reprogrammed all of the facility's work robots and security terminators to protect him, with the native creatures of the planet as an additional layer of defense. Getting through the perimeter first, then reaching Arkos himself, is the mission.