Captain Yates is taken over by the super computer, BOSS, and ordered to kill the Doctor.
The Doctor speaks with BOSS, and finds out that it runs the company, controls Stevens and other key staff members, and is responsible for the polluting chemical process. The Doctor employs the liar paradox, a conundrum which will keep BOSS busy trying to find a solution, while he escapes. Unfortunately, he runs into Stevens and some guards before he can do so. He rejects the brain-washing technique that Stevens subjects him to – but Mike Yates is more susceptible and is converted into one of the computer’s slaves. After the Doctor escapes, Mike is sent to the Nutchutch to kill the Doctor. His conditioning is deep and only broken by the Doctor’s use of the blue crystal he brought from Metebelis 3. Meanwhile, Jones has worked out that the fungus Jo spilled on the slides is actually a curative and then sets off to stop her, but they are both caught in an RAF bombing raid intended to kill the maggots. Cliff is also infected with a maggot and begins to turn green — before he was able to share his knowledge of the cure. In a delirious state, he utters the word ‘serendipity’. Yates re-enters Global Chemicals, pretending to still be under BOSS’s control, but he is caught by Stevens, who tells him he just can’t depend on anyone.