Who could be sending anonymous letters to some of the residents of Peterswood? Who could be so spiteful? Even timid Gladys, Pip and Bets housemaid receives one of these anonymous letters. The Find-Outers set about trying to solve this mystery, and even manage to get to look at some of the letters, and discover they were all posted from the small market town of Sheepsale. It's all just a matter of time now before the children discover who the writer is, but Mr. Goon is also close on their heels