A plot to steal a top-secret instrument vital to the United States space program poses a challenging case for Frank and Joe Hardy. After rescuing a South American stowaway who mutters a warning about "Footprints " and then vanishes, Frank and Joe discover that documents belonging to their famous detective father are missing and that footprints linger under a window. The young detectives search for the diabolical mastermind of the "Footprints" spy ring takes them on a flight to a group of islands off the coast of South America.
Franklin W. Dixon is a pen name used by a variety of authors writing for the classic series, The Hardy Boys. The first and most well-known "Franklin W. Dixon" was Leslie McFarlane, a Canadian author who contributed 19 of the first 25 books in the series. Other writers who have adopted the pseudonym include Christopher Lampton, John Button, Amy McFarlane, and Harriet Stratemeyer Adams.