Valuable electronic parts containing platinum are being stolen from shipments made by Stanwide Mining Equipment Company's cargo planes, and Frank and Joe Hardy are called upon to assist their world-renowned detective father to solve the baffling case. At Stanwide the boys pose as employees, and become suspicious of their boss's hostility toward them. Is he involved in the racket? And what is the truth behind the plane crash at sea in which Clint Hill,...

When a crime syndicate takes over Bayport's reservoir Frank and Joe Hardy help their detective father solve the sinister mystery.

Frank and Joe, the Hardy boys, solve a mystery involving a magician, American secret agents, an international spy ring, and a Scottish castle.

When Frank and Joe try to get hold of a top secret invention, they are put on the trail of jewel thieves and smugglers. Joe is kidnapped and Frank starts off on the chase.

Helping in a case their father is working on, the Hardy brothers try to find an informer who has telephoned from a booth in their home town, and are hired by a carnival owner to spot pickpockets.

Their SOS ignored in a storm, the Hardy boys find a wallet containing two thousand dollars alongside their boat and are launched into a mystery involving diverse clues.

While searching for the guard end of a broken saber that will solve one mystery, the Hardy brothers become involved with a gang of bank robbers.

The Hardy boys and two friends take a camping trip to the Rocky Mountains in an attempt to locate a gang of credit-card counterfeiters.

The Hardy brothers' visiting Greek pen pal enlists their help in searching for a priceless ancient Greek helmet loaned to and lost by a Hollywood movie company years before.

The Hardy boys' investigation of a museum robbery in England arouses the anger of a coven of black witches.