The Poisoned Hand by Agatha Christie

"Good air, a quiet life, no work. "That's your prescription." Following this doctor's advice, recovering pilot Jerry Burton and his sister Joanna decide to move to Lymstock. It was a quiet rural town, cut off from the world, where nothing ever happened and where they knew no one. Instead of living a calm and peaceful everyday life, they find themselves in the middle of events: anonymous, angry letters, suicide, murder... Each of the seemingly harmless and kind villagers is a potential criminal. Only Miss Marple's keen mind, with its keen understanding of human nature, will be able to uncover the truth.