With the car-theft case behind them, Frank and Joe Hardy are wondering what will happen next when a summer afternoon on the water brings them a new mystery. A man has gone missing, and the trail leads the brothers and their friends Chet and Biff to a series of caves where someone has been hiding and where a secret waits to be uncovered.
An early Hardy Boys adventure of 1929 in its original text, for readers who grew up with the series. Download the free EPUB.