Four years before Silent Parade (2022), Yukawa and Kusanagi investigate the murder of a writer after a video found in his possession piques Yukawa's interest.

Physicist Manabu Yukawa returns to Japan from America. Detective Kaoru Utsumi visits him and talks about a case. The case is about a popular girl in a town who disappeared and, several years later, her body was found. A suspect was arrested for her murder. That suspect was previously arrested for another girl's murder, but he was released due to a lack of evidence. Detective Shunpei Kusanagi investigated the prior murder case. The same suspect was then released due to a lack of evidence for the most recent murder case. The released man returned to his town, where everybody hated him. On the day of the autumn festival parade, the man was killed. Physicist Manabu Yukawa, Detective Kaoru Utsumi and Detective Shunpei Kusanagi work together on his case.