The Doctor and Romana receive a distress signal and arrive on Chloris. It is a lush and verdant world with only small quantities of metals, all of which are controlled by its ruler, Lady Adrasta. Adrasta keeps order with the aid of her Huntsman and his Wolfweeds – mobile balls of vegetation. A band of thieves, led by Torvin, organise raids on her palace to steal whatever metal they can. But in the mines of Chloris is something huge, a creature thrown into the pit to be forgotten… and the Doctor is about to join him.