Frank and Joe Hardy become involved in an intriguing mystery which revolves around their fencing master, Ettore Russo. Proof that Russo is the rightful heir to his grandfather s estate hinges on retrieving the guard end of a broken saber lost many years ago in California. The young investigators quest is complicated by a bank robbery during which some of their father s important records are stolen. A chase ensues in the grape-growing region of California as the boys engage in a dangerous game of hide-and-seek with the bank robbery gang.