"The Mystery of the Spiteful Letters" is the fourth book in Enid Blyton's "The Five Find-Outers" series. Fatty, Larry, Daisy, Pip, and Bets, along with their loyal dog Buster, find themselves embroiled in a case when anonymous spiteful letters start circulating in their village of Peterswood. The letters contain shocking secrets about the recipients, including their maid Gladys, whose parents are revealed to be thieves. Determined to uncover the truth, the children create a list of suspects, including nosy Mr. Nosey and gossip-loving Miss Tittle. However, they must race against their rival, the village policeman Mr. Goon, to solve the mystery before he does.