a worker named Elgin, an old friend of Fell, tells him about Dai's death and the dying Bert. Elgin later follows Fell into a pumping control room, where Fell is pumping the oil waste from the main tank on level four into another tank. The security system then registers the Doctor and Jo's presence in the pipe. Fell, who has actually arranged for the waste to be pumped down the pipe into the abandoned mine workings, is initially reluctant to rescue the two in the pipe. Elgin convinces Fell to help him open the hatch, and the Doctor and Jo escape as the oil waste cascades down the pipe. Fell goes to see Stevens, complaining about a 'headache', and Stevens puts the headphones on Fell. A voice tells Stevens that 'Fell's 'processing' was a failure' and orders self-destruction. After Stevens presses a button on a control panel, Fell leaves the room and jumps off a balcony to his death. The Doctor, Jo and the Brigadier end the day with a meal of fungus at Jones' retreat, the "Nuthutch", but the frivolity is cut short when they hear Bert too has died. After everyone retires to bed the egg the Doctor brought back from the mine hatches out into a giant maggot. Escaping from the lab where the egg was left, the maggot first heads for Jo, but then jumps on and bites Hinks, sent to the Nuthutch by Stevens to steal the egg. The maggot escapes from the house into the dark, and Hinks quickly weakens as the poisonous "green death" infection spreads through his body. The next morning, the Brigadier has the UNIT troops lay explosives and detonate the whole mine pithead, to the Doctor's fury. This fails to trap the maggots in the mine, as they begin to emerge; first, attempting to escape up the Global Chemicals waste disposal pipe, then burrowing through the slagheap near the mine. At Global Chemicals, Mike Yates has been sent in undercover by the Brigadier, and is contacted by the Doctor, who dons some improbable disguises in order to get through the gates and move freely. Having liaised with Yates, the Doctor learns that Stevens takes his instructions from someone on the top floor of the complex, and heads up there in the special lift to find out who is in charge. He discovers that this is the home of the BOSS,