Sixteen years after Caroline Crale is convicted of poisoning her painter husband Amyas and dies in prison, her grown daughter approaches Hercule Poirot with a letter in which her mother swears she was innocent. Poirot agrees to reopen a case that has long gone cold, knowing the physical evidence is gone and that only memory remains. He seeks out the five people who were present in the house on the day Amyas died, each of whom watched the events from a different angle and carries a different stake in what is remembered. Poirot asks each of them to set down a written account of that summer, and the same afternoon is told again and again, the versions overlapping, contradicting, and quietly concealing. From these competing recollections Poirot must reconstruct not just who held the poison but the tangle of jealousy, attachment, and loyalty that surrounded a marriage strained by the arrival of a young woman determined to take Amyas for herself. The story unfolds across two timelines, the present-day inquiry and the reconstructed past, and turns on character and motive rather than alibis and clues. It is a study of how people misremember, how they shield themselves and others, and how truth survives in fragments. Poirot weighs each account against the others, listening for the slip that tells him which witness has been honest and which has spent years protecting a secret.