Continuing from the previous episode, Shinichi tries to remember what was the case of that specific date and then remembers the case in the cabaret club. The case begins where Ran and Shinichi in disguise were spying on Kogoro with Takagi (since they need access to the club). They notice a famous professor, Mine Mashito with Kumi while Kogoro with Kyoko. Soon it was game time, Kiss-Kiss Derby in which both Kogoro and Mashito was selected. The game rules are that both men takes turns, receiving kisses from the 20 ladies who are lined up then pour wine into their glasses. The winner will be given a special kiss from Kumi. During the game, both men get kisses from the ladies (which infuriates Ran). The winner happens to be Mine and once Kumi drank the wine, she was about to kiss when she collapses. Shinichi checks on her and sadly she has already passed away. During investigation, it reveals that Kumi has died from drinking wolf's bane that was inside Kyoko's container. However, Kyoko denies it as she doesn't know it at all. Shinichi notices the line-up draw on the white board and sees that Kyoko was No.16. He deduces that the culprit must be a whiz in maths since the game only lets the contestants choose between 1 and 3, there's higher chances that the poison was in Kyoko's wine. Oddly, all the girls seem to be very happy that Kumi's gone, even going so far as to take down the picture. As the investigation progresses, Kogoro suspects it was Mashito but Shinichi proves that it was Kazuyo who poisoned Kumi. The proof is that she knows one of the lines that mathematician Rene Descartes says, in which Mine knows about it since Mashito told her. Her motive was that she had fallen in love with Mashito since last Christmas as she's the only person who talk as serious as she does. However, she overhears Kumi's conversation that she's planning to cheat Mashito with his money and plans to murder Kumi to protect Mashito. As she's been taken away while Mashito cried in grief, Kog
小五郎の浮気調査をするために、変装した新一と蘭は高木刑事とともに、キャバクラ「クリスティ」に潜入していた。店ではNo.1キャストである久美とのキスを賭け、小五郎と数学者の峰によりゲームが行われていた。久美は勝者となった峰から渡されたワインを飲み干し、キスしようとしたが苦しみだし絶命。峰を巡り対立していたNo.2キャストの響子が持っていたワインのデキャンタからは、トリカブトの成分が検出された。蘭に毒針が打たれ、「ゴフンイナイニ ゲドクザイ ヲ ウタネバ シヌ（5分以内に解毒剤を打たねば死ぬ）」のメッセージの後にキーワード入力画面となる。入力したキーワードは「デカルト」。直後に解毒剤を取りに行った小五郎が別室に閉じ込められるが、解毒剤は新一に手渡され、蘭は助かる。
