The Doctor and Romana arrive on the lush world of Chloris, a world with an overabundance of plant life but a lack of metal. They are captured by the tyrannical Lady Adrasta, who controls the planet's metal supply, and throws her opponents into an old mine to be devoured by a fearsome creature. The Doctor falls into the Pit while attempting to escape - how will he deal with the creature and defeat the cruel Adrasta?