Kim Gi-taek, a dedicated and determined cop, is on the verge of giving up on his job due to the lack of support from his superiors. Meanwhile, Jang Tae-sung is a ruthless gangster who runs a nightclub and is involved in various illicit activities. When Kim Gi-taek and Jang Tae-sung cross paths, they form an unlikely alliance to catch the serial killer.
When the Gangster becomes the only person to ever survive an attack by the Devil, he reluctantly teams up with the Cop. Their deal is simple: whoever catches the killer first gets to deal with him according to their own rules—the Cop wants an arrest, while the Gangster wants bloody revenge.
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