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.
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...
The strangled dead body of Hiroshi Hatano, accounting section chief at the longstanding apparel company Edaka International, is discovered in his apartment in Tokyo. At the scene, Inspector Totsugawa and Detective Kamei find out that a mysterious email stating "I'll be riding the Super Ozora 5 tomorrow" was sent to the victim's cell phone the night before. The sender, Manami Furuya, an employee of Edaka International's Planning Section, has strangely terminated her cell phone service and hasn't shown up to work that very morning. Immediately afterwards, Totsugawa is astonished to receive a report from the Hokkaido police stating that the body of a man, stabbed to death, has been found on the Super Ozora 5 limited express. The man is Yuuki Nakamura, a bar employee from Tokyo, who seems to have flown from Haneda Airport to Sapporo and then boarded the Super Ozora 5, which connects Sapporo and Kushiro. Totsugawa has the feeling that this can't be a coincidence...
