For 60 years, the group of detectives known as "Detective Office 5" has raised the bar for detective work. The agents of Detective Office 5 are a group of stellar detectives lead by the genius code breaker Detective 507. When an unknown client enlists 507 to crack his most difficult programming code yet, the detective embarks for Shanghai where he crosses paths with a sniper, an informant, the head of the Blue-Dragon Mafia, and beautiful singer on the run, Meilan. As 507 stumbles deeper into a twisted quagmire of intrigue he discovers the sad truth behind the mystery.

Inugami Sahei, who built up the wealth of the Inugami Clan, passes away, leaving a will with Furudate, his legal adviser, for his daughters Matsuko, Takeko and Umeko, all of whom have different mothers, and for their sons, as well as for Nonomiya Tamayo, the granddaughter of a person to whom Sahei feels heavily indebted. The will states that all his assets are inherited by Tamayo alone, on the condition that she marries one of the sons of the daughters. Furudate's assistant learns the content of the will, and seeks advice from Kindaichi Kosuke, a private detective, as he senses the air of unease. Shortly afterwards, murders start to occur one after another in the clan.

With the help of a six-inch-tall ancient samurai warrior, a lonely young environmentalist finds self-confidence and new companionship in protecting Japan's beautiful naturality from human mismanagement.