The secret of the old mill

by Franklin W. Dixon

"The Secret of the Old Mill" by Franklin W. Dixon is a mystery novel written in 1927. Brothers Frank and Joe Hardy investigate a dangerous counterfeit money ring in their hometown of Bayport. When mysterious warnings threaten their family and clues lead to a renovated mill owned by a secretive defense contractor, the young detectives must unravel connections between suspicious bicycle deliveries, fake bills, and a guarded facility. As they follow leads involving a teenage errand boy and strange nighttime activities, danger closes in around them.