柯南在街头目睹一名正打电话的警察在雨中被射杀,忙将凶手追踪,但凶手逃脱。死者闭眼一刻紧抓左胸,似乎有所暗示。事后柯南从目暮警官口中了解到紧抓左胸是暗示那里有警察手册。不久又有警察手拿警察手册被人射杀于地下车库。对于这两起案件,目暮警官等人一反常态不愿向毛利小五郎及柯南透露太多信息。毛利不甘心进一步追问,白鸟警官只答一句“Need not to know”。该话是警察之间所用的密语,意味这两起杀人事件与警察内部人士有关。
柯南、小兰等人参加白鸟妹妹的婚宴,电突然间停掉,那刻小兰正与女警佐藤在洗手间。小兰拿起身边的手电筒欲照明时,一颗子弹射进佐藤身体,小兰吓昏过去。次日小兰醒来,却因怪责自己害佐藤挨枪失去记忆。目暮见事态越来越严重,将秘密说出,原来死去的两名警察正与佐藤一起重查一桩有关医生仁野自杀的案件,该案涉及到警察局长的公子。将局长公子假定为嫌疑人之一时,柯南亦想到佐藤被射杀后宴会上少掉的两个人。
While visiting her friend Marjorie Attfield, Miss Marple learns that her son Bobby had recently found a body, identified as a Mr. Pritchard, on the cliff side. He's received a letter asking him to appear at the enquiry but it seems to be a wild goose chase meant to keep him away from the real enquiry taking place elsewhere. Now accompanied by a friend, Frankie Derwent, they trace the dead man to nearby Castle Savage, home to a dysfunctional family with great deal of money. The family patriarch, Jack Savage, had died not long ago and the dead man had some connection to the Savages. But what is the key to solving the mystery of Pritchard's last words to Bobby as he lay dying: "Why didn't they ask Evans?".