a supercomputer with its own megalomaniacal personality. It runs the company, controls Stevens and other key staff members, and is responsible for the polluting chemical process. The Doctor rejects the brainwashing technique that Stevens and the BOSS subject him to – but Yates is more susceptible and is converted into one of the computer's slaves. After the Doctor escapes, Yates is sent to the Nuthutch to kill the Doctor. His conditioning is deep, and is only broken by the Doctor's use of the blue crystal he brought from Metebelis Three. Jo has alienated Jones, with whom she is falling in love, by ruining one of his experimenting slides of green slime. Determined to make amends, she heads to the slagheap in search of a maggot to run some tests on. Meanwhile, Jones finds that the fungus powder Jo spilt on the slides is actually a cure for the "green death" infection. He races to the slag heap to find Jo surrounded by giant maggots, and they are both caught in an RAF bombing raid on the maggots. Jones is infected with the 'green death' and begins to turn green — and all before he was able to share his knowledge of the cure. Jo contacts her UNIT friends with her radio, and the Doctor and Sergeant Benton rescue the two from the maggots in Bessie. Hearing Jones utter the word "serendipity", the Doctor realises that Jones might have stumbled upon something that could combat the maggots and their infection. Benton arrives with a maggot chrysalis—proof that the maggots are beginning to transform into mature giant insects. Then, the maggot that escaped from the laboratory is found on the table—dead. Realising that the creature died from eating some of the fungus, the Doctor also discovers the cure for Jones. The Doctor and Benton drive around the slag heaps, scattering the fungus, which proves deadly to the maggots. They are then attacked by a giant fly creature—the mature adult form of the maggots—which the Doctor kills by throwing his cloak over it when it is in mid-air, causing it to get tangled in it and fall to the ground. The Doctor returns to Global Chemicals to confront the BOSS. The computer plans to link up with others and effect a corporate takeover of the human race. By now, Stevens is completely under the computer's control. The Doctor tells Stevens that the BOSS'