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.

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.

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.