Set in the summer of 1917, the story follows the war-wounded Captain Hastings to the Styles St. Mary estate of his friend John Cavendish. The Cavendish household is wrought with tension due to the marriage of John's widowed mother to a suspicious younger man. In the village, Hastings runs into his old friend Hercule Poirot and, when the estate's trouble turns deadly, the friends unite to solve a most baffling case.