The experiences of a mouse-colored horse from his birth in the wild, through his capture by humans and his work in the rodeo and on the range, to his eventual old age.
When Mr. Hardy disappears while investigating a mystery surrounding a vacant house rumored to be either haunted or an abode for criminals, Joe and Frank search for the truth.
During their search for members of a notorious gang responsible for a payroll robbery, Joe and Frank Hardy encounter timber wolves, a Rocky Mountain blizzard and a mine cave-in.
Joe and Frank suspect there is a link between the counterfeiting case they are investigating, and the case their father can't discuss. Determined to learn the secret, the Hardy Boys get themselves into a scrape.