Conan and his friends discover the bodies of real estate company president Kawai Shinzo and his former employee Shibata Kensuke in Shinzo's home.

After the body of Otaro's former partner Kyujiro is found, Otaro is found dead in a locked room at the Hatobue Lodge. It becomes clear that Otaro was one of two culprits wearing Byun masks responsible for the robbery and murder that happened seven years ago. It also comes to light that Manager Yuri Asako's daughter Miona was the witness in the case. The police believe Otaro died in his room accidentally after killing Kyujiro to keep him quiet, but... While investigating Otaro's room, Conan closes in on the truth...