波洛接到侦探小说家奥利弗太太的电话，邀请他去德文郡的一个乡村庄园。富翁乔治爵士安排了一个游园会，请奥利弗太太设计了一个类似寻宝游戏的破案游戏。但奥利弗太太始终觉得那有些不对劲，于是她请波洛以为游戏颁奖的身份来到了庄园。在这，波洛认识了乔治爵士，一个有着乡绅风度的富翁，他的太太，一个只知道衣服珠宝、被人认为“低能”的漂亮女人，迈克，一名建筑师，弗利亚特太太，庄园的前主人，莱利夫妇等人。波洛在与他们的交谈中，并未发现有奥利弗太太所说的异常之处。游园会当天清晨，乔治夫人收到了一封信，写着她的表哥将乘游艇过来，顺便探望她，这封信引起了乔治夫人的紧张不安。下午，游园会进行的很热闹，有很多人赶过来，包括住在附近青年旅游公寓的一些外国青年。破案游戏也照常进行，只是奥利弗太太似乎把它搞得太复杂了，以至于几乎没有人可以取得进展。最后，奥利弗太太决定和波洛一起去看一看装扮成“受害人”的那位姑娘，不料当他们来到设定的案发地点时，却发现姑娘真的死了

Distant cousins and childhood friends Elinor Carlisle and Roddy Welman are happily engaged to be married. One day Elinor receives an anonymous letter in the post, claiming that someone is trying their hardest to work their way into the affection, and subsequently also bank account, of her wealthy aunt Laura Welman, who is presently bedridden at her home since after a stroke and from whose death Elinor and Roddy both expect to inherit a large fortune. Not knowing what to make of the letter, the young couple eventually decide to pay Laura a visit in order to see for themselves what is really going on at the house. When they arrive, Elinor immediately becomes suspicious towards Mary Gerrard, the lodge keeper's daughter, recently returned to England after having studied in Europe and whom everyone else at the house seem to absolutely dote on. No one else however seem to share Elinor's suspicions or dislike of the young woman, and in particular not Roddy, whom Elinor one night discovers kissing Mary Gerrard in her aunt's drawing room. When Mary suddenly turns up dead, poisoned by a salmon sandwich, Elinor's dislike of Mary makes her the obvious suspect and hardly has time to take in what has happened before she finds herself on trial and condemned for murder. The only person who is not entirely convinced of Elinor's guilt is Doctor Peter Lord, who decides to contact his old friend Hercule Poirot in order to help him prove her innocence.

故事发生在风景如画的度假胜地意大利，正在享受自己难得的假期的波罗（大卫·苏切特 David Suchet 饰）邂逅了名叫帕梅尔（Frances Low 饰）的女士，后者声称自己是波罗的超级粉丝，并且热情的邀请波罗和自己一起享受这段度假时光。之后，波罗和帕梅尔又认识了两对同样在此休憩的夫妻，他们一对拥有雄厚的财力，另一对刚刚结婚，还沉浸在新婚燕尔的幸福之中。随着时间的推移，波罗渐渐察觉到这两对夫妻间藏着另一端古怪的关系。
就在波罗准备结束自己的休假之际，凶杀案发生了，年轻的瓦伦蒂娜（Annie Lambert 饰）死于中毒，而波罗亦背负上了莫名其妙的罪责被限制了行动。于是，被迫留下的波罗决定和帕梅尔夫人联手，破获凶案的真相。

波洛侦探（大卫·苏切特 David Suchet 饰）接到了莱蒙太太（保琳·莫兰 Pauline Moran 饰）的电话，邀请他去她家里做客。莱蒙太太的丈夫是国防部官员，他邀请了名为乔安娜（Carmen du Sautoy 饰）的女人去家中小住。莱蒙太太对这个女人的印象极为糟糕，她坚信她正在策划一个阴谋，一个同国家机密息息相关的阴谋。
拗不住莱蒙太太的坚持，波洛勉强赴约。让大家都没有想到的是，当晚，一份机密文件不翼而飞，乔安娜则成为了最大嫌疑人。当所有人都将矛头指向乔安娜的时候，波洛发现了事件的漏洞，他坚信事情一定不是表面看上去的那么简单。

培杰蕾夫人（阿曼达·沃克尔 Amanda Walker 饰）坚信自己的丈夫想要致自己于死地，并且在除掉她之后和他那金发碧眼的漂亮助手结婚。为此，培杰蕾夫人找到了波洛侦探（大卫·苏切特 David Suchet 饰）向他求助，可是，当波洛赶到康沃尔时，培杰蕾夫人已经死了，这让波洛感到非常的懊悔。
家庭医生告诉波洛，培杰蕾夫人死于胃炎。培杰蕾夫人的侄女福莱达（Chloe Salaman 饰）亦否定了培杰蕾夫人对于丈夫出轨的种种猜想。但对此，家中的仆人却是完全另一种说法，在他们口中，男主人对待女主人一直都算不上好。尽管众说纷纭，但波洛侦探还是很快就理清了自己的思绪，锁定了最大的嫌疑人。