Valuable electronic parts containing platinum are being stolen from shipments made by Stanwide Mining Equipment's cargo planes, and Frank and Joe are called upon to assist their world-renowned detective father solve the baffling case. While posing as Stanwide employees, the boys look into the truth behind the chief pilot's death at sea. The puzzling trail of clues leads the young sleuths to an uninhabited Caribbean island, but the final, and most startling, discovery is made in the boys' home town of Bayport.