A top-secret KX20 mini-computer is stolen from Healy Automation by Dreisenberg agents and plans are made for the ambassador to smuggle it from the country. Diplomatic immunity leaves the police and Secret Service powerless to act. The only chance of retrieving the mini-computer lies with Special Agents Father Stanley Unwin and Matthew Harding.

Father Unwin employs a unique device to shrink Matthew down to two feet tall and transports him in a specially designed suitcase to London Airport, where Father Unwin poses as a member of the maintenance staff in order to get Matthew close to the plane that will carry to Ambassador back to Dreisenberg the following morning.

In his miniturised form, Matthew sneaks aboard the plane through an open panel in one of the port engines. He manages to remain undetected during inspections the next morning, and the plane takes off with him on board.

Using specialised radios, Matthew and Father Unwin are able to contact each other, and Father Unwin sets off to rendezvous with the plane at Oakington Airfield.

On board the plane, Matthew shuts down one of the engines on the plane. The pilot makes the decision to return to London. Matthew then shuts down a second engine, and the plane is diverted to Oakington Airport in order to make an emergency landing.

Father Unwin collects Matthew from the plane, before the Ambassador opens the door of the plane. Father Unwin uses the Minimiser to shrink the Ambassador, then demands the return of the computer in exchange for returning the Ambassador to his normal size. The Ambassador's aide denies all knowledge of the computer, but the Ambassador pushes the case containing the computer over the edge of the plane and into Father Unwin's car.

Returned to his normal size, the Ambassador and his aide steal a police car and set off after Father Unwin. Matthew manages to keep them at bay by shooting at them whilst Father Unwin heads for home and safety.

Father Unwin manages to shake the Ambassador at the gate to his house, and the computer is returned to its rightful owner.

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