Detective Jung Tae-suk (Kim Mu-yeol) is a Cowboy Cop. He is dissatisfied with the rampant corruption on the force that allows organized crime to operate almost in the open, and the lack of respect officers get. This is made only worse when he realizes a serial killer is operating in his region and the surroundings, but lacking firm evidence and fearing Jurisdiction Friction, Da Chief refuses to treat the murders as anything but isolated incidents.
Jang Dong-soo (Ma Dong-seok) is a brutal mob boss with a penchant for brawling, who recently had to put a weaker rival back in his place. As he drives home alone one evening, he's attacked by the serial killer, but manages to fight him off. Eager for revenge, and wanting to remedy the loss of face his hospitalization caused, he sends his men to find the killer. While he has the manpower, he lacks the scientific and crime expertise the cops has, and soon makes an offer to Jung Tae-suk: He'll give Jung the manpower he lacks to pursue the killer, while Jung provides the expertise, and they will share information. If Jung finds the killer first, Jung can arrest him. If Jang gets the killer first, he'll gruesomely kill him in revenge to show what happens to those who cross him. Sensing there's no other way to stop the killer who has so far operated in the shadows, the detective accepts.
Little do both parties know that the killer is not done, that he has plans of his own, and Jang Dong-soo's own criminal dealings are about to make the situation way more complicated.
On 5 May 2019, it was announced that Sylvester Stallone will produce an american remake of The Gangster, The Cop, The Devil, with Ma Dong-seok reprising his role as Jang Dong-soo.
The Gangster, The Cop, The Devil contains examples of:
- Cowboy Cop: Jung Tae-suk, who raids criminal organizations against his boss' order. Has no patience or care for procedure.
- Enemy Mine: Jung Tae-suk and Jang Dong-soo. The former has gone out of his way to annoy the later and hinder his criminal activities. But as neither can see a way to stop the killer without the other's help, they are forced to cooperate.
- Evil vs. Evil: Jang Dong-soo is not a nice man. He's introduced having just unleashed a No-Holds-Barred Beatdown on someone as a work out session. He brutalizes his allies, underlings, and enemies without a thought to maintain his image and his position. He'll have a man killed in his bed for getting a leg up on him. Despite all this, he's still the lesser of the two evil when it comes to stopping the serial killer.
- Go-Karting with Bowser: The cops and gangsters actually start hanging out as they work the case, having lunch and drinking together.
- Made of Iron: Jang Dong-soo. The man takes a BEATING through the movie, and shrugs it off. By his own account, most people wouldn't have survived the attempted murder on his person.
- Pet the Dog: Jang Dong-soo gives a schoolgirl waiting for the bus his umbrella, encouraging her to keep studying. He's enraged when the killer murders her that same day.
- One-Man Army: Jang Dong-soo again. The man basically takes out 2/3 of Hur's gang solo, with barely a scratch.
- Taking You with Me: Jang Dong-soo's willing to go to prison, if it means the killer won't escape his crimes.
- Oh, Crap!: Kyung-ho has this reaction twice at the end of the movie. First when Jang arrives at the same prison and looks at him, and lastly when Jang approaches him with a rope in his hands. Both times Jang has a Cheshire Cat Grin on his face