It was an open and shut case. All the evidence said Caroline Crale poisoned her philandering husband, a brilliant painter. She was quickly and easily convicted and sentenced to life in prison. Now, sixteen years later, in a posthumous letter, Mrs. Crale has assured her grown daughter that she was innocent. But instead of setting the young woman's mind at ease, the letter only raises disquieting questions. Did Caroline indeed write the truth? And if she didn't kill her husband, who did? To find out, the Crale's daughter asks Hercule Poirot to reopen the case. His investigation takes him deep into the conflicting memories and motivations of the five other people who were with the Crales on the fatal day. With his keen understanding of human psychology, he manages to discover the surprising truth behind the artist's death.

琼是个彻底务实的人，从小只想过安稳的日子；她挑有前途的律师结婚、阻止丈夫追求田园生活，也要求三个孩子都依她的价值观去做人生规划。一次探望小女儿的返程途中，火车因雨季路断而停开，她受困沙漠中的一个小站，每天只能在附近沙丘散步，走着走着，她开始面对自己，一件件以往刻意忽略的“小事”这时都不请自来……
本书初版于1944年，是阿加莎·克里斯蒂一生最满意的作品之一。她藉本书满足了一个对自我的提问：我是谁？我“真正”是个什么样的人？我所爱的人对我有何想法？他们对我的想法是否如我所想？过程峰回路转，真实而残酷。