A cryptic message from their famous detective father and a note secreted in a ventriloquist's dummy lead Frank and Joe Hardy on a dangerous search to the tropical islands in the Caribbean. There the teen-age detectives are constantly beset by vicious henchmen of a criminal mastermind. Danger stalks the boys' every move, once in an isolated sugar mill, another time in a shark-infested sea. To add to their hazards, one of the young henchmen closely resembles Joe and fiendishly makes use of this strange coincidence. Through their resourcefulness and deductive reasoning, the brother sleuths ingeniously fit together the pieces of the baffling puzzle. The climax of this exciting mystery, when Frank and Joe come face to face with the ghost at Skeleton Rock, will be as much of a surprise to the reader as it was to the young detectives themselves.