The narrative begins when Dick, Tom, and Sam Rover, three upright and athletic brothers living at Valley Brook farm, lose their way on a mountain excursion and stumble into a hidden cave. This accidental discovery leads them to uncover a secret stash belonging to a local freight-thieving ring. Soon after, their simple lives are disrupted when their uncle, Randolph Rover, falls victim to a clever swindle involving unregistered traction company bonds, masterminded by unscrupulous men named Merrick and Pike. The brothers launch their own investigation, tracking the criminals through perilous mountain paths, country roads, and eventually to a wild west show and the city of Ithaca.
Alongside their usual school life at Putnam Hall—where they contend with a malicious new bully named Tad Sobber and navigate humorous misadventures with classmates like William Philander Tubbs and Songbird Powell—the Rovers remain determined to recover their uncle's stolen fortune. Their efforts ultimately lead them to an old abandoned homestead by the lake, where a confrontation with the thieves results in a dramatic boat chase and the dramatic recovery of the missing bonds. The book concludes with the brothers successfully finishing their studies at Putnam Hall, celebrating their graduation with old friends and sweethearts, and looking forward to new adventures.
