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...