Left in charge by Sanders, Security Man Hindle - unhinged and in complete control of the two Kinda hostages - locks up the others while he primes the dome for a 50 mile perimeter of deforestation through acid and fire, having "reasoned out" that the trees and plants are a threat. Adric perpetrates a ruse to help the Doctor and Todd but is caught and about to be punished when Sanders returns, a changed man. Sanders bears a gift for Hindle - a box given him by a Kinda mystic elder, which may be dangerous and which the Doctor is forced to open. Meanwhile, Tegan is shown herself in the dream world and left to determine which of her selves is real.

With a frightening vision of what's to come from Panna (the Kinda's blind visionary), the Doctor must break Hindle's control over the Kinda hostages and stop his deforestation plan, then send the Mara back to The Dark Places of the Inside from whence it came before it can destroy the Kinda and head out to topple civilizations.