The Secret of the Old Mill by Franklin W. Dixon

When the full story of the activities of the counterfeiters became known next day, Bayport found that the Hardy boys had succeeded in breaking up one of the most dangerous bands that had ever baffled the Federal authorities.

After the capture of Uncle Dock and his associates, Fenton Hardy and the Secret Service men had wasted no time. Frank had remembered the New York address of the mysterious Burgess, that he had heard Uncle Dock mention, and a telegram to the New York police resulted in the arrest of this man, who turned out to be the brains of the gang, the man who had arranged for the distribution of the spurious bills. The crooks in Barmet village, and the rascally woman in black were also apprehended.