A Healey KX20 mini-computer has been stolen by Dreisenberg agents and is believed to be in the hands of the Dreisenberg Ambassador, who plans to leave the country with the device. Father Unwin leaves immediately for Heathrow to plant a miniaturised Matthew aboard the Ambassador's private jet.
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.
£1 million in used bank notes is travelling to London by express train. One attempt to steal the notes has already been made, so the Bishop assigns Father Unwin and Matthew to protect the train's cargo. After the train is hi-jacked, Unwin finds himself unable to stop the vehicle as it hurtles towards London at 80mph.
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.
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.
Father Unwin discovers that a gang of bogus vicars are responsible for a series of sabotage attacks on military installations and vehicles. After one ofthe gang is hospitalised after their latest venture, Unwin masquerades as his replacement, a demolition expert, to infiltrate the gang, but he is soon exposed as an imposter.
The Bishop assigns Father Unwin to protect the King of Muldovia during his visit to London, joining his retinue for a flight to New York where the King plans to visit his son. An attempt on the King's life is foiled by Matthew, but the Prince of Muldovia has hidden a bomb aboard the King's private plane and rigged a device that incapacitates the pilot and co-pilot.
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.