"Drop case or else danger for you and your family." This warning addressed to Fenton Hardy not only alarms the famous investigator and his detective sons, but also puzzles them, because Mr. Hardy is working on more than one case. Which one prompted the threat? When more ominous warnings follow, Frank and Joe suspect there is a link between the counterfeiting case they are investigating and a secret case their father cannot discuss since it involves...

When the Hardy boys eagerly agree to assist their friend Jack Dodd and his father in locating a family treasure, the two young detectives are unaware of the baffling complications that will arise. The only clue to the long-lost treasure is a cryptic message written by a Pilgrim ancestor. But when Mr. Dodd and Jack are accused of stealing cars and then mysteriously disappear, Frank and Joe are confronted with a triple mystery. Have their friends run...

Frank and Joe Hardy are determined to bring to justice the vicious criminals who kidnapped their detective father while he was investigating sabotage of a road-building project in the Kentucky wilderness. After Mr. Hardy's amazing escape, the boys pick up a clue -- the word "Felix" mumbled by their sick father in his delirium. When they discover that the dossier of a notorious ex-convict has been stolen from Mr. Hardy's files, the two young sleuths...

When thieves hijack a collection of stuffed animals from a county auction, Frank and Joe Hardy pursue the getaway care and are drawn into a thrilling mystery. When thieves hijack a collection of stuffed animals from a country auction, Frank and Joe Hardy pursue the getaway car and are drawn into a thrilling mystery. The recently acquired interest of their best pal, chubby Chet Morton, in taxidermy as a hobby adds fresh twists to the puzzle. At the...

The Hardy boys embark on another puzzling mystery when they try to discover who is stealing rare collections of ancient pirate treasure and smuggling them out of the United States.

When they journey to Alaska to help a friend who feels his life is in danger, the Hardy brothers find their own lives threatened.