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!

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!

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.