After the death of his beloved girlfriend, police officer Kyungjoon just wants to be left alone to water his house plants and catch criminals. But after a police investigation into a mysterious cult goes supernatural, Kyungjoon finds himself unwillingly caught up in a world of demons, succubi and monsters – and the worst of them all is a demon king calling himself “Lord Cain.” It turns out that in order to survive, Cain needs mana that can only be accessed through a “door” inside Kyungjoon. The problem is… how is he planning to open that door?

Jung Intae may be the first to admit he’s a psychopath to the school nurse (his crush), but he certainly isn’t the last. Consequently, Miss Kim’s been dealing with a lot of high school psychopaths… Not that any of them really fit the bill. But dig a little deeper and it seems like everyone at the school, including the faculty, is harboring a secret… Like Intae’s obsession with Miss Kim, and the anxiety Miss Kim seems overwhelmed by at times. Someone at the school really is a psychopath, but who?