PC Goon, the village policeman, is receiving anonymous notes and enlists his nephew Ern to help him discover who is behind them. But Ern soon realizes that detecting is more fun with the Five Find-Outers and joins forces with Bets, Pip, Daisy, Larry, Fatty and Buster the dog. Together they solve the mystery of the strange messages, put two jewel thieves behind bars and close the case of a twenty-year-old diamond robbery.