About the book: 2021 / Young detectives will have to unravel another tangle of a series of confusing events. Counterfeit twenty dollar bills have appeared in the city. There are many guesses, but practically no evidence. True, one clue leads the Hardy brothers to an old mill, which serves as a passageway for a modern plant. There is something at this mill, but it is almost impossible to get there. And then the brothers decide to take a risk…