On a distant barren planet, Storm Mine 4 trawls across bleak deserts and through fierce dust storms in search of rare and valuable metals. Onboard the Sandminer is a small skeleton crew, who alternate between indulgent relaxation and skilled mining work. The mundane day-to-day duties of the mine are attended to by a much larger complement of servile robots.



This is a society that is dependent on robots for all areas of life, the people comforted by the knowledge that the strictest safeguards are built to each and every robot's programming. So when one of the miner crew is murdered, suspicion falls on two new arrivals.



The Doctor and Leela arrive on board, and are immediately accused of being the prime murder suspects. But the Doctor soon realizes that perhaps the killer isn't human. More deaths occur: can he persuade the remaining crew members that the killer is a robot?