Poison in the Pen - Miss Silver #29.
Poison in the Pen first published in 1955.
When the quiet village of Tilling Green plagued by an outbreak of poison pen letters, and then a mysterious suicide, Scotland Yard dispatches Miss Silver to investigate.
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, 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. He brings Miss Silver along as an undercover agent. He masquerading as a tourist as she attempts to stop the next death before it happens.
Patricia Wentworth--born Dora Amy Elles--was a British crime fiction writer.
She wrote a series of 32 classic-style whodunnits featuring Miss Silver. The first of which published in 1928, and the last in 1961, the year of her death.
Miss Silver, a retired governess-turned private detective, sometimes compared to Jane Marple, the elderly detective created by Agatha Christie. She works closely with Scotland Yard, especially Inspector Frank Abbott and is fond of quoting the poet Tennyson.