Dixon, Franklin W

Who is writing threatening notes? How could anyone get into the secret room of the old mansion? As Frank and Joe investigate, robbery and mistaken identity complicate matters.

False robbery charges, Joe's disappearance, and other strange things occur when Frank and Joe set out to retrieve their father's important papers from a diver.

The Hardy brothers embark on a freighter trip under mysterious circumstances and find themselves involved with a smuggling ring.

While in New Orleans during Mardi Gras, the two young sleuths try to track down the perpetrators of a rash of burglaries.

The Hardy boys accompany a Canadian teenager to Los Angeles to help locate a missing rare coin, but soon become involved in an even larger case.

The Hardy boys travel to Vermont to investigate a mysterious fire and to help a circus owner who is plagued with accidents.

On a visit to Germany the Hardy brothers investigate the theft of plans for a newly invented submarine and the mysterious disappearance of valuable coins and paintings.

Their search for an Easter Island idol takes the Hardy boys to Easter Island and on to investigate the theft of government material in Antarctica.

Frank and Joe go to Florida to investigate the sabotage of a satellite launch and uncover a theft ring involving sea animals.

Valuable antique weathervanes are being stolen in the Pennsylvania Dutch country. A Navy employee removes a top secret document from the Pentagon. The Hardy brothers try to solve these two seemingly unrelated mysteries.