Hercule Poirot is called in by his crime writer friend, Ariadne Oliver and discovers that she is troubled. She has been asked to create a "Murder Hunt" game for a fair at Nass House and she is puzzled with all the help she is getting. Poirot and his assistant, Captain Hastings arrive at the fair to see what is going on. They find a couple on the brink of divorce, a rich Lord and a dizzy Lady, an old lady, trapped in the horrors of the past and a womanizing architect. Things take a turn for the worse when during the "Murder Hunt" the girl playing the "dead" body is murdered for real, an old man's body is pulled from the local lake and the Lady of the manor goes missing when a face from her past shows up. It is clear to Poirot that someone is playing the game for real and he sets out to discover who it is... 20年的秘密。 喬治爵士和史達柏夫人，是一場鄉村園遊會的主辦人。除了豐富美食，算命遊戲、康樂活動等應景節目，他們還突發奇想，想在園遊會中舉辦一場謀殺遊戲。 知名的犯罪小說作家阿蕊登˙奧利薇夫人出於善意，同意為他們構思這場緝兇遊戲。她計劃在史達柏夫婦的納塞莊園佈下重重線索，並安排14歲的小瑪琳充當「受害者」躲藏於河邊的船屋，準備給大家一個意想不到的答案…… 然而經過一番縝密的規劃，奧莉薇夫人卻於最後關頭打電話向他的朋友赫丘勒˙白羅求助。因為她出於直覺，嗅到了不祥的預兆。她對白羅說： 「如果弄假成真，發生了真正的謀殺案，我也不會感到意外……」
