Trapped deep below ground, the Doctor and Jo discover the mine’s terrible secret.
The Doctor and Jo are trapped between a cave-in and the pool of maggots. They escape by wheeling a mine cart through the maggots, but they are still trapped in the mine. Back at Global Chemicals, Stevens is behaving very curiously. He is using strange headphones to listen to calming messages and when one of his employees, Ralph Fell, looks helpful to the environmentalists, he is somehow reconditioned with the same headphones and shortly afterward kills himself. Elgin saves the Doctor and Jo from drowning in the green slime when he helps them out of a shaft that links the mine and the factory complex — proving the link between the two. The Brigadier’s plan to investigate Global Chemicals further is cut short when he is ordered by the Prime Minister himself to let Stevens get on with it. Stevens evidently enjoys Cabinet support for his factory and its new plastic production process. The Doctor, Jo and the Brigadier end the day with a nourishing meal of fungus at the Nuthutch, but the frivolity is cut short when they hear Bert too has died. As the Doctor leaves, a maggot egg he brought back from the mine hatches, and the maggot inside creeps up on Jo, the girl none the wiser.