Joe and Frank decode a message that leads them to try and make a drop at the warehouse, despite the fact the message was intercepted by Police Chief Ezra Collig. The drop goes awry, but later when the boys return looking for more clues, they find a piece of fabric that the person fleeing the warehouse left behind. When the Tall Man escapes from the hospital, the boys reveal their entire investigation to their friends and get their help to lure the Tall Man to Chet's farm.
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.