After barely surviving a brutal attack by a sadistic serial killer, crime boss Jang Dong-su is left humiliated. Determined to catch the killer known as K, he forms an uneasy alliance with Jung Tae-seok, a relentless and incorruptible detective who often disrupts his illegal business. However, while Jang Dong-su wants K dead, Jung Tae-suk is determined to bring him to justice. With a deal in placeāwhoever finds K first will decide his fateāthe hunt begins, blurring the lines between crime and law.