Two British-designed desalination plants have exploded as they neared 250 hours of operation and an order for ten plants in the United States now hangs in the balance. Suspecting sabotage, the Bishop assigns Unwin and Matthew to ensure that the last remaining plant, at Port Trennick, stays operational.

Suffering from sunstroke, Father Unwin is retired to bed and prescribed sleeping pills by Dr. Brogan. In his fevered dreams, Unwin finds himself on a dangerous mission to deliver medical supplies to Bishopsville, flying in Gabriel to Africa where he and Matthew are captured by natives and attacked by mercenary fighter jets.

Professor Soames has developed a sonic rifle, capable of projecting destructive waves of ultrasonic vibration, accurate to within a centimetre over thirty feet. But three unscrupulous saboteurs intend to use Soames' rifle to bring down an experimental aircraft, holding the Professor's daughter hostage to ensure his complicity. When Father Unwin becomes suspicious and investigates, he too is held prisoner in Soames' house.

Sakov, one of Europe's most astute freelance agents, is trailed by Blake to Greenways Nursing Home, a health farm run by chief therapist Dr. Klam, and the Bishop assigns Father Unwin to find out what his plans are. Sakov engineers the crash of a GK2 test car at a nearby race track, but Unwin is baffled as to how he managed to escape the confines of Klam's theray theatre to carry out his sabotage.