Frank and Joe feel that the solution to a counterfeit case and one their father is investigating is hidden in an old mill that is used for making secret parts for missiles.

Frank and Joe investigate numerous crimes in their town that may or may not be related.

Frank and Joe solve a mystery involving the disappearance of a professor, a hot-tempered hermit, sabotage at the new Bayport Coastal Radar Station, and the Honeycomb Caves.

The Hardy brothers try to find out who is behind a rash of automobile thefts that are occurring on Shore Road just outside of Bayport.

When Joe's water skis go missing on a school stip to Lake Poketoe, he and his brother Frank try to solve the mystery.

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.

In solving the mystery of two medallions missing from an inherited curio collection, the Hardys wind up in a desolate area of Guatemala at the mercy of dangerous thugs.

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.

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.

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...