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.

When the Hardy Boys set out to solve the mystery of their missing chums, they discover a gang hide-out in a cave on an island along the way.

When their detective father asks them to play burglar in order to protect a client's valuable invention from thieves, the Hardy boys find themselves involved in a large and dangerous conspiracy.

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

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.

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

When the Hardy boys eagerly agree to assist their friend Jack Dodd and his father in locating a family treasure, the two young detectives are unaware of the baffling complications that will arise. The only clue to the long-lost treasure is a cryptic message written by a Pilgrim ancestor. But when Mr. Dodd and Jack are accused of stealing cars and then mysteriously disappear, Frank and Joe are confronted with a triple mystery. Have their friends run...

The Hardy Boys have the honor of handling one of the giant balloons in the Bayport Fall Festival parade. But the day before the parade, the balloon is ripped, and everyone thinks Joe did it. Can the brothers find out who the real culprit is?

"Bayport Elementary's annual science fair is here, and Frank, Joe, and their friend Phil are determined to win. But the morning of the fair, Phil discovers that their awesome homemade robot has gone missing!"--Page [4] of cover.

"Eating candy nonstop and watching TV all day sounds great . . . until you actually do it, as the kids of Bayport High find out when all the adults vanish, and the world's greatest (high school) detectives--the Hardy Boys and Nancy Drew!--have to team up to solve the mystery! Whether it's going under cover, sneaking out at night, chasing weird buses, or following a strange smell, they know it'll take all their wits and smarts to get their parents...