Frank and Joe Hardy suspect that their best friend Chet Morton is the victim of a summer school swindle and offer to help get his money back. While probing a baffling burglary at the Seneca Indian Reservation in New York State they investigate Zoar College located nearby. A startling connection between the Zoar College swindle and the theft of the Seneca’s gold tribal relic Spoon Mouth propels the teenage sleuths into a series of perplexing and dangerous situations.

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 detective’s 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.

A banker who has been receiving threatening notes enlists the help of the Hardy boys. Before long, the young sleuths find themselves entangled in the investigation of a notorious band of thieves.

Timber wolves, a Rocky Mountain blizzard, and a mine cave-in are only a few of the perils Frank and Joe Hardy encounter during their search for the principal members of a notorious gang responsible for a payroll robbery. Clue by clue, Frank and Joe cleverly fit into place the scattered pieces of this dangerous puzzle and come up with the astonishing solution.

When Frank and Joe Hardy receive a telegram from Tony Prito in Alaska telling them that his life is in jeopardy, they immediately make plans to fly to Tony’s rescue. Unknown enemies dog the Hardys and their pal Chet Morton even before they start the 4,000 mile journey. Puzzling questions lead the Hardys into dangerous sleuthing in the wilderness of Alaska and British Columbia. The astounding secret that the young detectives uncover, in the shadow of the forbidding mountain peak Devil’s Paw, winds up one of the most perilous adventures they have ever encountered.

Tony Prito enlists the help of his detective friends Frank and Joe Hardy when a sinister stranger demands that Tony sell him the bizarre curio collection he has just inherited. While the boys are discussing this suspicious incident, the stranger, Valez, telephones and threatens Tony. That same afternoon the three boys collect the cases of curios at a freight station only for Joe’s life to be at risk on their way back to Tony’s house. The next day a seaman claims two medallions in the collection that coincidently go missing. Did Valez steal them? And what was their significance. Unraveling the clues in this exciting mystery takes the Hardys and their friends to a desolate region in Guatemala and straight into the hands of a gang of dangerous thugs.

With only the slender clue of an arrow-shaped tie clasp, Frank and Joe Hardy pick up the trail of a cunning gang of thieves responsible for a wave of jewelry-store holdups. But their investigations are interrupted when a desperate plea for help comes from their widowed cousin who lives on a cattle ranch in New Mexico. Frank, Joe, and their pal Chet fly there immediately, and manage to put an end to the trouble at the ranch and solve the jewelry-store robberies.

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.