Frank and Joe Hardy are investigating a mysterious old house high on the cliffs above Barmet Bay when they are frightened off by a scream. The boys return to the apparently haunted house when they make a connection between the place and a smuggling case their father is working on. When their father goes missing, they have to investigate the caves beneath the house and confront the smugglers.

Frank and Joe race against time to retrieve a scientist's top-secret invention before thieves get their hands on it. But the young detectives soon discover that they are involved in a mystery far greater in scope than just safeguarding the invention. When Joe is kidnapped, this incident starts Frank of on a chase that could end disastrously for him and his pals.

Caught in their motorboat the Sleuth by a sudden storm at sea, Frank and Joe Hardy are relieved to see the lights of a yacht. But their SOS ignored. The shrill sound of a siren fills the night air and moments later a helicopter drops an object alongside the Sleuth: a wallet containing two thousand dollars The next day, a truck carrying a shipment of high-powered rifles has been stolen. These two apparently unconnected events are clues in a tangle of mystery which turns out to be one of the detective brothers' most exciting adventures.

A cryptic message from their famous detective father and a note concealed in a ventriloquist's dummy lead Frank and Joe Hardy on a dangerous search to the tropical islands in the Caribbean. There the teenage detectives are constantly beset by vicious henchmen of a criminal mastermind. Danger stalks the boys' every move, once in an isolated sugar mill, another time in a shark-infested sea. But when Frank and Joe come face to face with the ghost at Skeleton Rock, it will be as much of a surprise to the reader as it was to the young detectives themselves.

When dogs and men suddenly disappear, and strange screams fill the night, fantastic stories of vengeful ghosts are almost believable. It is these strange happenings which bring Frank and Joe Hardy to the Pocono Mountains to help their father's friend solve the mystery of Black Hollow. But when the Hardy boys and Chet Morton arrive at Captain Thomas Maguire's cabin on the edge of the hollow, he has disappeared. Frank and Joe are determined to find the captain, despite Chet's misgivings after a night of weird and terrifying screams. Strangely, it is a small puppy that discloses a most unusual...

The handwritten will of a deceased world-traveler is strange and mysterious. Its cryptic instructions are to deliver "the valuable Aztec warrior to the rightful owner, a descendant of an Aztec warrior." Frank and Joe Hardy have only one slim clue to work with: the name of a complete stranger who can help. Despite the harassments, the threats, and the attacks made upon them, Frank and Joe unravel clue after clue in their adventure-packed search for the living descendant of the mighty Aztec nation which once ruled in Mexico. It takes as much high courage as clever deduction for the young...

Rarely do magicians reveal their professional secrets. Consequently Frank and Joe Hardy are amazed when a well-known magician, the Incredible Hexton, offers to reveal the secret of his "Vanishing Man Act" and invited Mr. Hardy to be the subject. When their detective father fails to reappear, his sons are convinced that something sinister is afoot, despite Hexton's insistence that Mr. Hardy is playing a joke on them. While desperately searching for their father, Frank and Joe find themselves working with SKOOL, a U.S. organization of secret agents pitted against UGLI, an international ring of...

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.

Why is a wealthy sportsman so frightened by the serpent design on a mysterious balloon that he begs Frank and Joe Hardy to protect him? And who stole the ancient life-size chess king which is to be presented to the winner of the world chess championship? Targets of diabolical enemies, Frank and Joe find a clue that leads them across the Pacific to Hong Kong to help the police smash an international criminal organization.

There is not time for explanations when Mr. hardy telephones Frank and Joe form the West Coast and sends them flying off to England to help his old friend Professor Rowbotham. Their stay in East Anglia begins with a weird omen, as they witness the bizarre funeral of an old witchmaster. From then on, strange things happen. When the Hardys learn about the strange disappearance of Lord Craighead, the plot deepens. Danger follows them to Ireland as Frank and Joe survive a shipwreck and find a clue from a frightened white which that leads to the torture chamber of a black witches' coven, all in...