A freshly-retired Senior Police Officer, Yamazaki Yoshiyuki (Tsuruta Shinobu) is found dead. In Yoshiyuki’s hand is the classified section of the magazine, and a handkerchief that is believed to belong to the assailant.
Yoshiyuki's wife Yoshie Yamazaki (Yasumi Maesawa) and his son Yamazaki Satoru (Ryō Hashidzume) are not sure why Yoshiyuki would have been interested in the classified section of the magazine. Yoshiyuki’s wife and his son knew that Yoshiyuki was devoted to his police career and that he had a strong grudge against his father who was responsible for his mother’s hardships.
Investigator Miyuki Oda (Shihori Kandjiya) discovers that before Yoshiyuki’s death, he went to visit an employee at the Japanese Music Acoustic Laboratory named Natsuko Etō (Maki Mizuno) to apologize for a case 18 years ago, which involved Yoshiyuki’s colleagues, Senior Chief Police Officers Saita and Kagami. In the past, Saita (Hatsunori Hasegawa) and Tōru Kagami (Ren Osugi) assigned Yoshiyuki to instruct the Police Dog Academy.
The investigators find out that Yamazaki was helping Ōta Susumu (Chiyo Shōta) look for a job since he was on probation, but the handkerchief remains a mystery to the team. Itomura uses one of the police academy dogs to aid him in the investigation. Where does the police dog take Itomura? How does this case relate to Ota and the case 18 years ago?