A scout troop investigates the disappearance of a child that leads into a layered mystery involving break-ins, a suspicious stranger and an apparent spy. The boys follow clues, trail suspects, endure a head injury, and confront thieves, leading to capture, a dramatic escape and a lakeside confrontation. They contend with false alarms, parental concern and skeptical police while unraveling the cryptic significance of a recurring white card. Gradually their deductions and teamwork expose motives and tie disparate incidents together, resolving the mystery through discovery, cooperation and decisive action.