Frank and Joe are called upon to find a wealthy industrialist’s son who has mysteriously disappeared. The only clue in the case leads the two young detectives to South America, where the intrigues of evil adversaries almost cost them their lives. Only through their courage and perseverance do the Hardys solve one of the toughest cases they have ever tackled. | Hardy Boys 51: The Masked Monkey by Franklin W. Dixon, Paper over Board | Indigo Chapters