Determined to learn the secret of the old mill, Frank and Joe employ a clever ruse 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.
Determined to learn the secret of the old mill, Frank and Joe employ a clever ruse 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.
