Did Graham Retson flee from his home because he was at odds with his father, or was he kidnapped? Finding the answer turns into something more dangerous and larger in scope than Frank and Joe ever bargained for. 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. Involved in this complex mystery are a fierce-looking monkey trained to be a killer, a school of voracious, man-eating piranhas, a ruthless gang of passport thieves, and a cleverly operated change-your-identity mill for criminals.
Only through their courage and perseverance do the Hardys solve one of the toughest cases they have ever tackled.
- San Marten
Additional details on the monkey
The monkey had a mask on, with earphones linked to 'San Marten, the main ringleader, who told the trained monkey what to do. Whenever the mask was off, the monkey was very friendly to everyone - indicating that the mask had turned him into a criminal prop.
- Manaus, Brazil
- Belem, Brazil
- Granite City
Businesses and organizations
to be added.
to be added.
- ↑ Who Wrote the Hardy Boys? at Keeline.com
- ↑ The Masked Monkey Major Edition Types at The Hardy Boys Unofficial Home Page
- ↑  'The Mysterious Case of The Masked Monkey ', Bayport Times #22, March 2000