When Shihoon was a child, his exorcist parents vanished in a fight with underworld spirits. After Shihoon has a chance encounter with the devil Mephisto, he somehow ends up contracted as the next judge for the legendary fight between archdevil Mephisto and the human, Faust. Along with his exorcist older sister, Shihoon enters the underworld to fulfill his contract and search for clues of his parents' disappearance.