Weary from his wife's repeated suicide attempts, the husband seeks help from a secretive agent who an old doctor introduced to him. In the middle of the night, "they" come to his house.
Major crimes unit detective Seong-jin arrests Tae-sung for petty crimes, but shocked to find out that he is the notorious serial killer. However, Seong-jin becomes doubtful of his identity as the serial murder case is investigated.