Frank and Joe unravel two mysteries, one involving a counterfeiting case and the other concerned with a national security case their father is working on.

On an ice-bound, snow-covered island, Frank and Joe attempt to solve the mystery of a boy's disappearance and the theft of a priceless collection of antique medals.

The search for a stolen boat leads the Hardy brothers to Mexico where they become involved with a band of Indians and a strange smuggling operation.

A disappearing floor, a savage-looking hound, a galloping ghost and a startling invention are just a few of the strange elements that complicate Frank and Joe's efforts to solve the mystery of the death of an heir to a mansion.

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.

Frank and Joe are confronted with the crisis of water disappearing from the reservoir at Skull Mountain.

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.

The Hardy boys find the missing deed to an Indians' land, prevent a phony salesman from carrying through a reckless scheme, and help their father solve a top-secret case.

Hired to locate an old Spanish cannon, the Hardy brothers uncover an even greater treasure after perilous underwater adventures.

Despite attempts against their lives, Frank and Joe accept a case involving the most powerful man in a small town in Georgia and an allegation of piracy and smuggling.