With two cases in tow, the Hardy boys look to Turner mill for clues. Determined to learn the secret of the old mill, Frank and Joe employ a clever ruse to gain entrance, only to find themselves trapped. How the young detectives extricate themselves from this dangerous situation and unravel mysteries will keep readers tense with suspense

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 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. Deadly road traps, aerial ambush, a spider man and a suspect who carries a menacing cane harass the young detectives as they seek the triple solution to this perplexing and exciting mystery.

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.

In their motorboat the Sleuth Frank and Joe Hardy search Barmet Bay for a dangerous stranger who has stolen a valuable boat. Suddenly, in the eerie fog, they spot the craft drifting aimlessly out to sea. What happens next starts the young detectives and their pal Chet Morton on an intriguing adventure that takes them to Mexico and into the comparatively unexplored desert and mountain regions of Baja California.

In one of the most dangerous and intriguing cases of their careers, Frank and Joe Hardy help their father investigate a series of mysterious car accidents. Each of the drivers had seen a signpost marked DANGER shortly before his accident. The young detectives investigate, only to discover that the signposts have vanished. The attempted theft of a secret experimental motor and the kidnapping of a famous race horse are part of this thrilling case, which proves to be as sinister as the signposts themselves.

A blind peddler's warning and a weird glass eye plunge Frank and Joe Hardy into one of the most baffling cases they have ever tackled. The young detectives' investigation takes them to a walled estate guarded by savage dogs, where a wealthy businessman is hiding out in fear for his life. In a climax that will hold the reader spellbound with suspense, Frank and Joe find themselves trapped in a sinister house of mystery where there seems to be no escape

Strange events involve Frank and Joe Hardy in a mystery which shrouds an ancient treasure--the golden head of the Pharaoh Rhamaton IV. The owner of the million-dollar golden Pharaoh's head claims it was aboard the freighter Katawa, which sank not far from Whalebone Island. But suspicious developments indicate that Mehmet Zufar may be trying to defraud the shipping line's insurance company. Frank and Joe enthusiastically accept the challenge of their famous detective father to assist him in investigating the complex case for Transmarine Underwriters.

A series of museum thefts launch the Hardy Boys on this baffling mystery. Rare collections of ancient pirate treasure are being stolen, so Frank and Joe are asked to stake out the Black Parrot, a suspicious freighter docked in Bayport Harbor. This whirlwind chase after a self-styled pirate king in the Caribbean stronghold of the Empire of the Twisted Claw makes a gripping tale of suspense and high adventure.

There is a crisis in Bayport Soon the city will be without water Every night, water strangely disappears from the new reservoir near Skull Mountain. Frank and Joe Hardy join forces with a team of skilled engineers to solve the baffling mystery.