Wales, the near future. While the Doctor finally gets to visit Metebelis Three, Jo and UNIT investigate a spate of strange deaths near Global Chemicals' plant. What effect has the company's toxic waste had on the local wildlife?
The Doctor and Jo discover the mine’s terrible secret. But a giant maggot hatched from an egg that the Doctor brought back from the mine is on the loose.
Investigating the old mine workings, Jo and miner, Bert, have become trapped beneath the surface.
Cliff and the Doctor work to find a way to destroy the green maggots. Time is running out as they emerge from the mine to menace the entire area.
