A ferocious, wolf-like creature appears during the night of the full moon in a small Adirondack town, attacking livestock and scaring many of the residents. A young man with a history of werewolves in his family line is suspect. Joe barely escapes a horrible death as the young detectives solve this exciting and hair-raising mystery.

When a ferocious, wolf-life creature appears in a small town, the Hardy boys are engaged to clear the name of a young man who has a history of werewolves in his family.

When a man selling leather goods door-to-door steals the key to their detective father’s file cabinet, Frank and Joe Hardy set out to track him down. An odd mark on a key case which the man sold to their mother leads the teenage sleuths to an Indian village, whose chiefs begs them to help him find valuable tribal possessions and the deed for his land. How Frank and Joe find the missing deed and Ramapan treasures, how they prevent the phony leather-goods salesman from carrying out a ruthless scheme and how they help their father solve the top-secret case he is working on for the U.S. government makes exciting reading for all fans of the Hardy boys.

Once again Frank and Joe Hardy take on a puzzling case when their famous detective father asks the boys to assist him in tracking down a notorious jewel thief and his accomplices. The trail leads to the outskirts of the Hardys’ home town and to a weirdly guarded mansion on the old Perth estate. With their pal Chet Morton, the brothers must tackle the mystery of the mansion heir’s sudden death. A disappearing floor, a huge, savage-looking, hound, a galloping ghost, and a college professor’s startling invention are just a few of the strange elements that complicate the boys’ efforts to solve both mysteries.

A dying criminal confesses that his loot has been stored "in the tower." Both towers of the looted mansion are searched in vain. It remains for the Hardy boys to make an astonishing discovery that clears up the mystery and clears the name of a friend’s father.

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 long-distance telephone call from Chet Morton’s uncle summons Frank and Joe Hardy and their staunch pal Chet to a summer art school, located near old Fort Senandaga which is reputed to be inhabited by a ghost. The young detectives’ assignment: recover two famous oil paintings stolen from the valuable Prisoner-Painter collection owned by Jefferson Davenport. Mr. Davenport reveals that one of the famous pictures contains a clue to the hiding place of a priceless gold chain. Vicious threats and deadly traps beset Frank, Joe, and Chet as they search for clues to the stolen paintings and the gold treasure – a search that is complicated by the stormy feud between an Englishman and a Frenchman over the military history of the ancient fort.

Not only is the local bank robbed, but two of the Hardy boys' pals mysteriously disappear after a masquerade party. Are the events related? How the Hardy boys use all their courage and skill to outwit the criminals provides an exciting climax to one of the most baffling mysteries the young detectives have ever encountered.

When the Hardy Boys take a winter vacation in Jamaica, Joe finds an ancient bronze death mask washed up near their beach house during a violent storm. Helping the Hardys and their friends in this bizarre mystery is William, a Jamaican boy, who flies to New York with startling news, only to be intercepted and held for ransom—the death mask! Frank and Joe must rescue William, plunge into their father’s airline-ticket theft case, and fly into a maze of danger in Africa.

Frank and Joe Hardy become involved in a case affecting national security when Joe dials a wrong telephone number and gets the Pentagon. Two words— “Bombay Boomerang”— that the boys hear before the line goes dead plunge them into a whirlpool of danger and intrigue. At the same time, Frank and Joe must save their father from a murderous gang stealing mercury shipments in the Baltimore harbor. With clues linking the mercury thefts to the top secret Super S missile mysteriously stolen from a government arsenal. In a race against time, the three Hardys foil a diabolical scheme to create widespread havoc in the United States.