When a serial killer strikes women who all have a similar appearance, the police department's Special Crime Investigation Team is stumped. While Cha Ji An (Jang Na Ra), an elite detective, and her fellow colleagues are assessing the latest crime scene, the mysterious Lee Hyun (Seo In Guk) shows up and instantly assesses the trademark attributes of the killer. Hyun is a genius criminal profiler with a degree in criminal psychology who received an anonymous email that brought him to the crime scene all the way from the United States. The serial killer seems to be sending a personal message to Hyun with the clues he leaves behind, and Hyun wonders if it could be related to an escaped criminal "monster" from his childhood who killed his father and was responsible for the disappearance of his younger brother. Ji An has known Hyun since childhood and is ecstatic to see her childhood crush again, but Hyun doesn't seem to remember her. With no leads to capture the serial killer, Ji An and her colleagues solicit ...