The boys once again have jumped into the thick of a complicated mystery. Samuel Blacksone and his brother Ruel Rand live on adjacent properties, and it appears that one of them is out to hurt the other because they are both attacked. Frank and Joe soon learn that treasure is rumored to be hidden between the two properties, and as they investigate, they learn that others are involved in the apparent plot between the two brothers. Spooky mansions, secret...

The Hardy boys and their father solve a mystery involving inexplicable crashes of highspeed race cars being used to test an experimental turbine motor.

The Hardy Boys encounter a weird hermit and a gang controlled by a powerful crime syndicate and search for a missing scientist on Skull Mountain.

After the new hydrofoil they are guarding is stolen, the Hardy boys face frequent danger in solving a mystery involving criminals who operate by signs of the zodiac.

When two suspicious plane accidents occur near an eastern airport, the two Hardy brothers investigate the case and find themselves in greater danger than they anticipated.

The Hardy brothers interrupt their investigations of jewelry-store holdups to answer a plea from their cousin on a New Mexico cattle ranch.

The search for missing gold takes the Hardy boys to the Yucatán Peninsula where they uncover a second mystery.

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

A chance meeting with a stranger on the road provides the Hardy brothers with a clue to a gang of local burglars.

Frank and Joe are in London and learn that a new voice transmitter that can be implanted in a tooth has been stolen.