After a devastating personal loss, Kyungjoon wants nothing more than to drown his grief in the silence and safety of his houseplants. But Kyungjoon is also a cop, and it's a cop's job to go after criminals.

One day, hot pursuit of a suspect leads to Kyungjoon discovering signs of cult activity. Soon, the policeman is caught up in the machinations of monsters and demons, the worst of which is the demon king, Lord Cain, whose survival in this world depends on mana that can only be accessed through a "door." Cain's door happens to be inside Kyungjoon, and these two will have to get up close and very personal to open it.