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.

The Hardy Boys are elated over their good luck when wealthy Elroy Jefferson invites them to spend Christmas vacation at his private retreat on Cabin Island. But when Frank and Joe make a reconnaissance trip in their iceboat, The Sea Gull to the island, a belligerent stranger orders them off. Why? Before twenty-four hours have passed, the Hardys find themselves involved in two mysteries: the first concerns the recent disappearance of Mr. Jefferson's

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The two young detectives solve a mystery involving a top secret government agency and a world-famous spy who wishes to defect to America.

The Hardy Boys are given clues which send them in search of the treasure hidden by the Outlaw of the Pine Barrens.

When the Hardys discover that someone wants to get Frank and Joe out of the way before the championship game, they decide to catch the saboteur before it is too late.

Frank and Joe agree to help prepare a new prehistory museum for its opening, but learn that a mysterious sabateur has made the dinosaur exhibit dangerous in hopes of driving the museum out of business.

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

When Frank and Joe join a volunteer project in the south of France, they hear that the ruined castle nearby may be haunted by the ghost of its lord, who was slain by bandits, and they wonder if the spooky events they witness are an attempt to sabotage their project.

The Hardy Boys solve mysteries related to a gang of terrorists and a stolen diamond.