Kobayashi and Inoue are trapped in the underground discharge channels as a result of Twenty Faces' maneuvering, and a massive amount of water is pouring into their chamber. Worried about the police officers searching elsewhere in the channels, Inoue tells Kobayashi to escape with the message that the map they were given is fake and they need to evacuate immediately. However, the officers still end up trapped. Hanasaki rushes to rescue them and talks the former Boy Detectives' Club member Katsuda into helping him get to the scene faster. But as they're en route, more and more water surrounds Inoue...
巡査長を捜しに水路へ入って行った小林と井上は、二十面相の策略によって閉じ込められ、大量の水を流し込まれる。井上は水路を捜索する警官達を心配して「水路の全体図が偽物とすり替えられているので、避難するように伝えろ」と言い、小林だけを逃す。が、警官達も水路に幽閉されてしまう。救出を急ぐ花崎は元少年探偵団の勝田に応援を頼み、共に水路へと駆けつける。しかし、その間にも水はどんどん井上を飲み込んでいき……。
Kobayashi e Inoue están atrapados en los canales de descarga subterráneos como resultado de las maniobras de Twenty Faces, y una gran cantidad de agua está entrando en su cámara. Preocupado por los oficiales de policía que buscan en otros lugares de los canales, Inoue le dice a Kobayashi que escape con el mensaje de que el mapa que les dieron es falso y que deben evacuar de inmediato.
절대로 사람을 죽이지 않는다는 이십면상의 룰은 쉽게 뒤집히기 마련. 이노우에와 코바야시는 익사할 위기에 빠지는데...
