Brothers Frank and Joe Hardy and their elementary school friends help them track down what they hope is a treasure after they find a mysterious map.

When Thrill Kingdom has a roller coaster design contest, Frank and Joe help their friend Phil with his model, but on the day of the contest someone ruins their entry and Frank Joe investigate to find the culprit.

Frank and Joe are the most promising contestants in the annual Junior Bike Race in Bayport, but when Frank accidentally runs over a nail a blows a tire, his bike disappears and everyone becomes a suspect.

The students at Bayport Elementary get ready to compete for Field Day, in which prizes will be offered to the winning grade and the student with the overall high score, but Frank and Joe uncover a mystery when they discover someone has tampered with the equipment the day before the competition.

Frank and Joe Hardy are suspicious of Max O' Malley, a new kid in town who claims to be a magician, and when Mrs. Briar's prized show dog arrives and Charlie begins to disappear and reappear, Max becomes the prime suspect.