When a lifeboat crew discovers a luxury cruiser adrift in the English Channel, they find on board are a group of wealthy pop stars and their girlfriends, one of whom is dead. Doomwatch investigate, and discover that the death was not from drug abuse as was previously suspected; instead they begin to uncover the facts behind the dumping of a deadly chemical warfare compound in a deep sea trench, which seems to be far from dormant.

Doomwatch are joined by Doctor Robson, sent to undertake tests on the new 'Sahara' spray which is apparently capable of destroying all plant-life on the planet. But when Quist receives a phone call from the ministry, he is given orders to immediately suspend both Robson and Toby without any explanation. Closer investigation leads Quist and his team to discover that a new computerised security system run by Commander Keeping and Barker has become far too powerful, and is making its own decisions about government personnel.

Dr Quist attempts to go on holiday, but gets involved instead in a series of jet engine experiments causing harm and the same mysterious hallucination.

Ridge and Hardcastle are sent on what seems a simple enough assignment, but stumble onto a major government cover up in an abandoned English manor.

Doomwatch become involved with the inhabitants of a small, secluded island who have been forced to leave for the English mainland and are struggling to survive.