A few months after the serial murder case targeting women with long black hair was solved, a new unidentified body was found at the same scene. In order to find out the truth, the traumatized detective Kagaya Manabu (Chiba Yudai) went to the serial killer Urano Zenji (Narita Ryo) who he had arrested before. "Did you kill him?" In response to Kagaya's questioning, Urano in prison revealed the existence of the mysterious person "M" whom he respected as his teacher. Soon, Kagaya learned that his lover Matsuda Minori (Shiraishi Mai) made a painful choice after being targeted by a mysterious man, so he decided to entrust Urano to assist in the investigation...