This is one of my favourite Poirot novels. It shows Poirot and his little grey cells solving a crime years after it was committed.
Caroline Crale was convicted of murdering her artist husband, Amyas Crale 16 years ago. Their little daughter was sent to Canada to live with relatives, but now she is an adult and wants to get married. She is concerned that having a murderer as a mother might put off her betrothed, and so comes to Poirot asking for him to uncover the truth about what happened. She is convinced her mother was innocent. So, Poirot sets off to talk with each of the people who were present when the poisoning occurred and to uncover the truth.
Each chapter tells the story from a different character's point of view. We discover unrequited love, illicit affairs, violence and passion, all set against the genteel backdrop of an English summer. It's marvellous stuff. If you are feeling particularly alert you can compare the evidence of each character and it should allow you to piece together what happened to Amyas Crale. If, like me, you just wanted to enjoy the journey with a nice cup of tea and a biscuit, that's OK too.