Set in the subterranean Mine-World, a gang of human laborers is held as slaves by the wicked dictator Zygon until one of them, Orin, unearths the hilt of a mythical sword that only he can wield. After fleeing the planet, he meets Dagg, a renegade smuggler, a pair of helping droids, and the princess, who join forces to return to the Mine-World with a plot to destroy Zygon and rescue Orin's oppressed people.