Conan and Ran accompany Kogoro to the mansion of a client, soft-serve ice cream maker Morikawa Yuzan. Yuzan has cancer and not long left to live and asks Kogoro to evaluate his three potential heirs. His third son Morikawa Yuzaburo is found dead inside a locked room. Furthermore, his second son Morikawa Yujiro, who had been missing since the previous day, is found dead inside the soft serve tank. His eldest son Morikawa Yuichiro breaks down, saying he's next, and locks himself inside his room.
