Franklin W. Dixon 
Trouble in Paradise [EPUB ebook] 

A mission for ATAC has Frank and Joe Hardy traveling the world. The teenage son of a prominent mid-eastern diplomat has gone missing on the Caribbean island of St. John, and the boys take off to find him. Turns out he’s been kidnapped by a group involved in a scheme to rob a sunken Spanish galleon of its treasures and sell them on the black market. Frank and Joe search high and low–fighting thugs and sharks–for clues. When the Hardys finally find their quarry, there’s another problem –he turns out to be the mastermind of the ring, not its victim!