Lonesome Road - Patricia Wentworth

Governess-turned-sleuth Miss Silver must follow a trail of poison-pen letters to save an heiress from murder. Rachel Treherne has always had a steady head on her shoulders; it's why her late father named her the sole trustee of his considerable fortune. But the decision galled a number of Rachel's relatives, including her married older sister, her socialist nephew, and her father's ambitious young cousin. Rachel fears she may be overreacting to the anonymous letters she's received threatening her life, but then someone tampers with the chocolates she bought herself. If her cousin hadn't partaken first and noticed an unwholesome taste, who knows what may have happened? Miss Silver suspects someone in Rachel's inner circle has grown tired of being a poor relation, and she travels incognito to the Treherne country home to unmask the culprit-before it's too late-in this intriguing entry in the beloved series featuring a contemporary of Agatha Christie's Miss Marple. Lonesome Road is the 3rd book in the Miss Silver Mysteries, but you may enjoy reading the series in any order.