Two brothers, Frank and Joe Hardy, await their father's return from a detective case but encounter a stranger who tricks them into exchanging a counterfeit five-dollar bill. Disappointed and embarrassed, they learn about a wave of counterfeit money circulating in their town. Their father, Fenton Hardy, investigates a larger counterfeiting operation, which leads the boys to suspect that the old mill on Willow River is involved. The brothers decide to investigate the mill, suspecting it may be a front for counterfeiting. They meet Lester, a boy living with the mill's owner, Uncle Dock, who reveals that he is not allowed to leave or attend school. The Hardy boys deduce that the mill is suspicious, especially since Uncle Dock keeps Lester isolated and does not allow him to see the machinery. One night, they sneak into the mill and discover a printing press producing counterfeit money. They overhear the men discussing their plans to escape with the counterfeit bills. After a close call with Markel, one of the men, the Hardy boys manage to escape and inform their father, who organizes a raid on the mill. With the help of local law enforcement, they capture Uncle Dock and his associates, who are revealed to be part of a larger counterfeiting ring. The Hardy boys receive a reward for their efforts, and Lester is taken in by a kind family, ensuring a brighter future for him. The story concludes with the promise of more adventures for the Hardy boys as they continue their detective pursuits.
By Franklin W. Dixon · First published 1930 · Genre: Mystery, Adventure, Young Adult · 25 chapters