Arriving on an arid planet, the Doctor and his companions encounter the Drahvins, a species stranded on the planet, which is soon doomed to explode. But the only functioning ship is in the hands of another mysterious species, the Rills.
With Maaga holding Steven as hostage, the Doctor and Victoria have no choice but to investigate the Rill's spaceship. There, they discover the operation behind the Chumbelys, and come face-to-face with the mysterious Rills.