The Mysterious Affair at Styles

Hercule Poirot, the brilliant-and eccentric- detective who, at a friend’s request, steps out of retirement- and into the shadows of a classic mystery on the outskirts of Essex. The victim is the wealthy mistress of Styles Court, found in her locked bedroom with the name of her late husband on her dying lips. Poirot has a few questions for her fortune-hunting new spouse, her aimless stepsons, her private doctor, and her hired companion. The answers are positively poisonous. Who’s responsible, and why, can only be revealed by the master detective himself…
(Excerpt from Wikipedia)