Patricia Wentworth 
Poison in the Pen [EPUB ebook] 

Miss Silver comes to the aid of Scotland Yard when a village is turned upside-down by cruel anonymous letters: ‘;A first-rate storyteller’ (The Daily Telegraph). It is through her friend Frank Abbott, of Scotland Yard, that Miss Silver first learns of the anonymous letters. A widowed cousin of his, living in a small country village, is being tortured by an unknown author who insinuates that the young woman’s husband may not have died of natural causes. It is a case of the kind of cruelty that is all too common in the countryside, and the governess-turned-detective listens with only polite interest.Then the first death comes. Another target of the letter-writing campaign, tortured by the threats to reveal her darkest secrets, drowns herself in the manor-house pond. The Yard sends Abbott to unmask the sinister letter-writer, and he brings Miss Silver along as an undercover agent, masquerading as a tourist as she attempts to stop the next death before it happens.