Fenton Hardy enlists his sons, Frank and Joe, to help solve a gold theft in Montana. The journey from Bayport to Lucky Bottom is fraught with obstacles, including the gang of thieves, mine disasters, a blizzard, and encounters with wildlife. They must also determine the rightful owners of the stolen gold. Despite dated language and stereotypes, the book offers a glimpse into America's past, showcasing innocence and warmth. In the end, the boys are hailed as real detectives.