Sakon Futatsuki is the newest addition to the Tokyo Metropolitan Police Criminal Investigation Unit. Alongside his elder brother, Ukon, he investigates a plethora of crimes while trying to uphold his own principles and morals. In contrast, Risa Aioi is a skilled detective who works in the same division, but she uses unconventional means to find and capture criminals. She has the tendency to fall madly in love with the targeted perpetrator and will resort to stalking them relentlessly until they turn themselves in. Sakon is appalled by Aioi's extremely questionable method of hunting criminals, even though it has a high rate of success. He is determined to get her to reconsider her approach to crime-fighting, but the more he learns about her past, the more reluctant he is to do so. At the same time, Aioi finds herself wanting to rein in her impulses because there is still a criminal she desires to capture above all. Concerned with the safety of his colleague, Sakon must learn how to fight "poison with poison" and control it before it is too late. [Written by MAL Rewrite] Included one-shot: Volume 3: Shinobi Shinobazu