On a desert planet the giant sandminer crawls through the howling sandstorms, harvesting the valuable minerals in the sand. Inside, the humans relax in luxury, while most of the work is done by the robots who serve them. Then the Fourth Doctor and Leela arrive – and the mysterious deaths begin. First suspects, then hunted victims, Leela and the Doctor must find the hidden killer – or join the other victims of the Robots of Death.