Bunsei era, at a time when Edo culture is at its peak, and barely 50 years before the arrival of the Meiji Restoration in 1868. Sabu is a cheerful, honest young man who left his hometown with the dream of becoming a policeman. He is an informant to the policeman Saheiji  of Asakusa in Edo and stays with him and his daughter Midori. One day, Sabu encounters the cool master swordsman Ichi, who makes a living giving massages, and they become partners in an unexpected way. Although Sabu is still an informant, he and the blind Ichi collaborate in a way that compensates for each other’s shortcomings. Sabu becomes Ichi’s eyes while Ichi becomes Sabu’s right-hand man and solves cases with his well-honed skills of deduction as they search for the truth in difficult cases in Edo. One case starts with the discovery of two dead bodies in the Sumida River. The bodies have diagonal slashes and were left in boxes.