Young-su is tired of an investigation with no progress, and creates a criminal behaviour analysis team by persuading detective Ha-yeong, who sees through the minds of others.
Ha-young faces dangerous criminals and struggles to see through them. He digs into the thoughts and intentions of those who commit evil crimes and follows in the footsteps of what made them fall into the abyss of evil.
A murderer who committed a crime against a wealthy elderly person disappears, and another murder case occurs that is similar but differs in method. Ha-young struggles to uncover the identity of the culprit.
Ha-young focuses on chasing after a brutal criminal, and the police struggle even more with the criminal whose tools and methods are gradually changing to vicious; Young-su looks back on his actions.
Ha-young, who finally faces Nam Ki-tae, tries to figure out his inner heart and the full story of the incident; the police begin to thoroughly investigate Nam Ki-tae's house; Nam Ki-tae's vicious heart is revealed.
A series of mysterious disappearances occur, and the police detect an unusual energy; Ha-young falls into a crisis, and Young-soo spends the day in pain because she thinks that what happened to Ha-young is because of her.