Rei Kiriyama, a professional shogi player and high school student who lives alone in an apartment, visits his shogi teacher Masachika Kōda in a shogi hall. After Rei wins a match against Masachika, Rei is contacted by his friend Hinata Kawamoto, who invites him over to her house across town for dinner. After picking up groceries from the convenience store, Rei is awaited by Hinata, as well as her older sister Akari Kawamoto and younger sister Momo Kawamoto. While eating curry for dinner, Rei hears on the news that the body of Shizuo Unagawa was found badly bludgeoned in his own house, in which his eldest son Tadashi, a university student, has been arrested after being suspected of murder...