Biff Brewster receives a mysterious, urgent telegram from his uncle, Charles Keene, from Martinique, asking him to come quickly. Biff's parents reluctantly allow Biff to make the trip. During the airline trip, Biff meets another boy, Derek, who looks like Biff. After making friends on the flight, they decide to play a trick on Biff's uncle by exchanging identities. The exchanged identity backfires as Biff is kidnapped by thieves hoping to find and steal a pearl fishery that Dere's father has discovered.

Andy Adams is the Grosset & Dunlap pseudonym for three writers who authored the Biff Brewster series of adventure and mystery novels for adolescent boys in the early and mid-1960s. Walter B. Gibson, Edward Pastore, and Peter Harkins were real-world authors.