When J.B. Cox offers Joe up to Gloria, he is hired to find the other two pieces of the Eye. Joe's lucky charm goes missing and Aunt Trudy uncovers the boys' investigation. Elsewhere, Fenton rescues Rupert Khan and learns what he and Laura were working on. Frank and Joe discover their mother's music box holds a secret.
After a family tragedy strikes, Frank Hardy, 16, and his brother Joe, 12, are forced to move from the big city to their parents' hometown of Bridgeport for the summer. Staying with their Aunt Trudy, Frank and Joe's quiet summer quickly comes to a halt when they discover their dad, Detective Fenton Hardy, has taken on a secret investigation. Realizing that their Dad may be on to something the boys take it upon themselves to start an investigation of their own, and suddenly everyone in town is a suspect.