The third Hardy Boys mystery begins with the boys being duped by a stranger at the rail station. They change a large bill for him, which turns out to be counterfeit. In the revised edition the brothers would never be so daft, so it was their chubby chum Chet who takes the fall.
Counterfeiting, the boys are informed by their father, is becoming a serious issue in Bayport, and up and down the Eastern seacoast. Mr. Hardy suspects that production may be centered near their own city! Meanwhile, the boys went on a fishing trip and discovered a disused mill is being repaired and put back into business. However, they aren't interested in Chet's father's business as their rates for milling are outrageous. A theory is floated about that they're developing a new breakfast cereal and are understandably hush-hush about it. Meanwhile they befriend the lonely young boy (after saving his life, natch) who lives tat the mill, and try to pump him for information. The biggest development is the boys finally getting a sweet motorboat for their very own, and naming it the 'Sleuth'.
There are some interesting chase scenes and additional character studies, but while the original 'Secret of the Old Mill' is superior writing, the mystery was too thin to recommend it very much. The revised book tried jazzing up the story with cleverly delivered threatening notes to the Hardy's, but also fails to gel. The original gets three and a half stars for fun slang and period details circa 1927.
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