The Doctor jams the spinning gears and has the Brigadier reverse the motor, even it destroys the machine. The lift grinds to a halt less than 20 feet from the bottom of the shaft. Jo and Bert, concerned about the cable, climb down.
The Doctor figures out a way to use the other lift to rescue Jo and Bert - but they will need cutting equipment from Global Chemicals.
Jo and Bert find Dai Evans, near death and glowing bright green.
Elgin agrees to loan the equipment but Stevens cuts him off and has his associate Fell "processed" by "our boss" so that he will tell the Brigadier they have no cutting equipment. Fell does as he is told, to Elgin's consternation. He confronts Fell, who is cold and robotic in his responses.
The Doctor finds that the lift was sabotaged. Bert remembers another exit in the mine and he and Jo set off for it.
When the Brigadier reports the lack of cutting equipment, neither Professor Jones nor the Doctor believe him. As the Brigadier leaves to find equipment, the two scientists decide to break into Global Chemicals.
Cliff stages a protest to distract the guards and the Doctor sneaks in. He is attacked by guards and knocks them out. But Stevens corners him and show him an empty shed, claiming the equipment was moved.
The Brigadier returns with a torch he found at a petrol station. They repair the lift and the Doctor and three miners descend.
Bert and Jo find a green glow and a rotten smell deep in the mine. They see a green ooze and Bert touches it.
The Doctor finds Dai dead, his body completely green. He find Jo's note and sets off after them with Dave.
Bert is turning green and sends Jo ahead to get help. The Doctor finds him soon after and sends him back with the miner.
Jo finds a cave filled with massive maggots wriggling in green muck. The Doctor catches up with her but the cave suddenly collapses, trapping them. Maggots slither out of the rubble and advance on them…