Signposts in the Night -A Record Surrounding a Certain Suspect-

In 1996, cram school teacher Togawa (Uno Shohei) was murdered by his former student Akutsu (Noda Yojiro), who suffers from mild mental disorders. Two years later, detective Taira (Yoshioka Hidetaka), who works in a secluded area, is ordered by the head of the criminal investigation division, Izutsu (Wada Masato), to reinvestigate the disappearance of Akutsu along with his subordinate, Oya (Takasugi Mahiro), but it seems that Taira is also struggling with some kind of problem. The fates of two seemingly unrelated people, Toyoko (Takiuchi Kumi) a supermarket clerk and Haru (Otani Kokai), intertwine, and the case begins to move again!

Taira and Oya, investigating the motive for Togawa's murder, begin by questioning those involved, starting with an assault committed by Akutsu (Harada Konosuke) when he was a junior high school student, but the mystery only deepens. Meanwhile, Toyoko, who is hiding Akutsu at her home, reunites with her ex-husband Sugiura (Kashiwabara Shuji), but her mind is unreadable. Meanwhile, Haru's classmate Sakurasuke (Kobayashi Masahito) learns that Haru cannot attend the school trip due to family circumstances and becomes worried about her... Wandering around a residential area hungry, Haru unexpectedly meets Akutsu.

Taira and Oya speak with Akutsu's ex-wife, Miwa (Asakura Aki), and learn that Akutsu had a deep affection for Togawa, but they are unable to find a motive for Togawa's murder. Taira and the others finally decide to speak to Akutsu's mother, Eiko (Kimura Midoriko), who has refused to be interviewed. Meanwhile, Haru, who has begun to open up to Akutsu, begins to visit him while Toyoko is away, but Sakurasuke witnesses the scene. Meanwhile, an unexpected tragedy befalls Taira's private life.

The actions of Taira's son, Takanori (Sakamoto Manato), weigh heavily on Taira's heart. While Taira tries to reexamine his own behavior through conversations with his wife, Sumiko (Emi Kurara), Oya makes contact with Sachiko (Bando Nozomi), a former student at Togawa Juku. They then discover the existence of a "Parents' Association" to which parents of Togawa Juku students also belong, but Taira and Oya are removed from their duties in the Togawa case... Meanwhile, a word spoken by Akutsu drives Toyoko to madness. What truth will Taira discover?

Akutsu is willing to take risks to make Haru's wish come true - upon learning of this, Toyoko takes action. Akutsu and Haru head for Nikko, the place of their dreams, but a certain person stands in their way. Meanwhile, Taira and Oya visit Eiko again and get closer to the dark side of the incident... Taira and the others learn that Akutsu has taken Haru to Nikko through a strange coincidence, and finally come face to face with Akutsu. What is the "dark side of society" that lies ahead as they discover the truth of the incident?