Serial killer Shinju Shinagawa , called "Shinagawa Pierrot" for her clown makeup at arrest 3 years ago, remained silent during her first trial. Child consultation center worker Arata Natsume suddenly gets a request from Takuto Yamashita, the child of one of the serial killer's victims, who informs him that he's been corresponding with Shinagawa in his name in order to find out what she did with his father's missing head. Arata pretends to be an elite civil servant but finds that the Shinagawa he meets is different from the one he expected. When she realizes he isn't the sender of the letters, she goes to leave. In a panic, Arata, who never planned on getting married, blurts out "Let's get married!"
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.