Crashing inside a newly formed planet, the Doctor and others find it inhabited by a slave labor mining society, where rocks are harvested for their radioactive energy and human life has little value. With a population controlled by deliberate cave-ins, poison gas, and periodic sacrifices to an Oracle, the miners, called Trogs, are also descendants from Minyos, and who desperately desire freedom.

With the Trog revolt close to success, the Oracle grants the Minyos travelers what they seek (the long lost race bank) in hopes they'll depart peacefully and straight away, but the Doctor suspects it's not all going to be as amicable as that. And what to do about the Trogs?