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.

Enemy agent George Grey is believed to be being hidden by the influential Sir Humphrey Burton at his country residence. Father Unwin pays Sir Humphrey a visit, enabling a miniaturised Matthew to discover that Grey is to be smuggled out of the house by helijet - if he effects a successful escape, he will take with him details of anti-missile defences and the locations of all reprisal bases!

Aerial photos of a secret experimental World Air Force fighter plane are being offered on the black market, so Father Unwin and Matthew are assigned to determine how the photographer has managed to breach the restricted overhead access to Crayfield airbase. Their investigations lead them to pigeon fancier John Masden, who seems an unlikely candidate for espionage.

Top secret plans to correct the orbit of the errant G9 satellite are falling into the hands of the opposition and sabotaged. The Bishop suspects that General Brompton is unwittingly leaking the information at his golf course, so Father Unwin tees off with the General to determine how the secrets are being passed to the other side.

The Aquatank, a new computer-controlled military vehicle, is to be demonstrated to the NATO heads of defence at the World Army Experimental Vehicle Division base. Anticipating sabotage, the Bishop assigns Father Unwin and Matthew to check security arrangements at the base, and Matthew is on board the Aquatank when it is re-programmed to target the oberservers' blockhouse!

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.

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.

Lord Edward and Lady Martha Hazlewell have inherited a counterfeit plate from their father, but the location of the second plate is known only to their father's accomplice, Mullins. Unwin and Matthew trail Mullins to Hazlewell Manor and join a frantic chase to retrieve the second plate from an old barn at Greenacre Farm.