Agatha Christie 
Mysterious Affair at Styles 

When the wealthy Emily Inglethorp is poisoned and the police get tangled, Poirot puts his prodigious sleuthing skills to work. There are several suspects, including the victim’s much younger husband, her resentful stepsons, her longtime housekeeper, a young family friend working as a nurse, and a London specialist on poisons who just happens to be visiting the nearby village. All of them have secrets they are desperate to keep, but none will fool Poirot.