Ryuuou Yamaguchi

Detective Kamei of the First Investigation Division receives a request from lawyer Shinichi Nakamura, the son of his deceased close friend, to re-investigate a car accident. Akiko, the wife of Yasuo Furuki, a painter from Hakone, died in the accident 5 months earlier by crashing into a guardrail. Nakamura's client, Akiko's younger sister Yuki Izeki, suspects that she was actually murdered by Furuki for insurance money. Overwhelmed by these thoughts, Yuki had sent an email reading "I'll never forgive that man. I'm going to kill him and avenge my big sister," announcing a murder to Nakamura. In the middle of their conversation, Nakamura receives a call from Hakone PD confirming that Yuki had turned herself in that morning...

Inspector Totsugawa of the First Investigation Division goes to Tsuruoka in Yamagata to attend the wedding of the son of Inspector Mukai, his former colleague who now works for the Yamagata Prefectural Police. While sightseeing at Mt. Haguro after the ceremony, he notices a young woman drawing him in her sketchbook. She introduces herself as Yuka Shiraishi and says she came to draw the Dewa Sanzan. Signing the drawing of Totsugawa next to the five-story pagoda with her initial, a 'Y' in the corner, she gives it to him as a present. The next morning, the corpse of a young woman who has been stabbed is discovered in a forest in Tsuruoka. When Totsugawa, on his way back, hears that a sketchbook signed with a 'Y' was found at the scene, he follows Mukai there. However, the body is not Yuka, the woman Totsugawa had met, and while no items pointing to her identity are found, the sketchbook is the same one Yuka had the day before.

Six high school tennis clubmates, including railroad investigator Noriko Hanamura, are going on a day trip to Kawaguchi Lake. However, one of them, Ayako Hirayama, does not show up even after the arranged time for the meet-up has passed. Magazine writer Yumi Tachiki, who planned the trip, calls Ayako but gets no answer, so Noriko and the others, believing Ayako will catch up with them, proceed to their destination. Even though Yumi and Noriko call Ayako many times, she does not answer. Yumi receives an urgent work request after arriving at Tenjozan Park by ropeway, so Noriko and the others return to Tokyo leaving Yumi at the mountain. None of them had any contact with Ayako the entire day. That night, Noriko receives a call from the Yamanashi Prefectural Police informing her that Yumi's body has been found stabbed in Tenjozan Park. One of the ropeway employees happened to witness a mysterious woman wearing a hat and a mask following Yumi down the mountain trail that evening...

The First Investigative Division is the star unit of the Tokyo Metropolitan Police Department. Jun'ichi Ōiwa, the head of the division, leads around 400 elite detectives. He has an extremely heavy responsibility: attends initial investigations at the scenes of all brutal crimes that occur within the metropolis, decides on the course of action of the investigations at the same time as he directs many investigation task forces and gets into investigations himself at the critical phase. However, Ōiwa is definitely not a superman. Amid his suffering, Ōiwa overcomes this grave responsibility and is quite simply a "life-size hero" and "ideal boss" to his subordinates.