The Secret Of The Old Mill thb-3

Read The Secret Of The Old Mill thb-3 Storyline:

Counterfeit money is in circulation, and the limit is reached when Mrs. Hardy takes some from a stranger. Then the Hardy boys and their high school chums are warned to stay away from the old mill. Their curiosity plunges them into peril of the most unexpected kind. ______________
Determined to learn the secret of the old mill, Frank and Joe employ a clever use to gain entrance and become trapped. There they unravel two mysteries, one involving a counterfeiting case and the other, a national security case their father is working on.