Making a forced materialisation on Chloris, the Doctor, Romana and K9 become embroiled in the political machinations of its ruler, the Lady Adrasta. The lush vegetation of the planet's surface hides a ragtag group of bandits, a giant eggshell, man-eating Wolfweeds and, within the depths of an old mining pit, something very large has a terrible secret which threatens the destruction of Chloris itself...