Poirot is asked to solve a poisoning that took place 16 years ago. A famous artist was poisoned, and his wife went to prison, where she died. Their daughter insists her mother was innocent. Poirot interviews 5 people who were at the scene, and we read 5 different versions of the event. Each one of them seems guilty, and Poirot solves the mystery in classic fashion. I enjoy the logic of Christie's plots.