The Hardy Boys in The Secret of the Old Mill by Franklin W. Dixon. A.J. Flynn-Branzell Period 2. Main Characters. Frank Hardy. Joe Hardy.
I believe that the counterfeit money has something to do with the old mill. It also seems that there are more people in the counterfeiting gang than just the four that are at the old mill.
The world is full of brand new mysteries to be solved and you could be the next one to figure one out!