在这部康沃尔谜案悬疑/犯罪片中,令波罗懊丧不已的是,他到达康沃尔太迟了,以至没能阻止蓓捷雷夫人的死亡—— 她曾经请求过他的帮助,因为她怀疑她的牙医丈夫正在对她下毒,以便他能与他那年轻的金发助手结婚。 蓓捷雷夫人的医生坚信绝不会有人想谋害她,有关她丈夫的绯闻纯属流言,她100%是死于胃炎;蓓捷雷夫人的侄女福莱达认为所谓下毒只是姨妈的胡思乱想,并声称姨妈生前竟然爱上了她的未婚夫!而福莱达的未婚未则怀疑下毒可能确有其事;家中的仆人更反映,蓓捷雷夫人丧生的前一天,她看见男主人手持险草剂站在餐桌旁,餐桌上正好放着蓓捷雷夫人的稀饭…… 经过不懈的抽丝剥茧的调查,波罗终于找到了正确的方向……
Poirot and Captain Hastings travel to Cornwall at the request of Mrs. Pengelly but arrive to find that the woman is dead. She had told Poirot the previous day that she feared her dentist husband, Edward Pengelly, had been having an affair with his pretty receptionist and that further, he was trying to poison her. Apart from her husband, she has a niece and her fiancé, but no other relatives in the village. When Inspector Japp arrests the husband for murder, the Belgian detective is convinced that the wrong person is in the dock.