After watching a video concerning Rena and Eisuke, Conan contemplates if the two could really be related after learning they have different blood types. He informs Jodie of what he learned, and considers that the Black Organization could be using Eisuke without him realizing it. Elsewhere, Shuichi Akai watches over Kir in the hospital which reminds him of a similar accident involving him and Shiho's older sister Akemi. The next day, Conan and the gang pay a visit to a mansion where Eisuke's deceased mother used to work to retrieve her effects, while Kogoro is introduced to an unsolved murder case.

Kakuzo Okudaira's wife, butler, and maid are interrogated about their actions prior to Kakuzo's murder. Eisuke discovers the photo of his mother missing and returns to the pool where he slipped and fell earlier to search for it. He finds it at the bottom of the empty pool and when he climbs back up, Conan realizes something that helps him solve the case. Back at the crime scene, Kogoro still believes Kakuzo committed suicide. Conan stuns Kogoro to use him to reveal the trick behind the murder and explain that Kakuzo's dying message points to Kikuyo the maid who also murdered Kakuzo's son the year before using a similar trick. Kikuyo confesses and explains she murdered them because they murdered their former butler.