Believer (2018)

Won-ho is a police detective attempting to bring down Asia's biggest drug cartel run by a man called Mr. Lee. He has been seen by no one, and as a result, a lot of drug dealers have been posing as Mr. Lee to conduct illegal trades. One day, when Won-ho is approached by Oh Yeon-ok, who has recently survived an explosion intended to kill her, Won-ho's team arrives at the site and finds a survivor.

When he is admitted to hospital and tries to escape in order to find out about the fate of his mom and pet dog, the police catch him and make him speak the truth. His name is revealed to be Rak, and he had been working in Lee's gang. Won-ho takes him to his dog and reveals his mother to be dead, causing Rak to team up with the police to seek revenge against the boss responsible for his mother's death and dog's poor condition. Rak and Won-ho arrange a meeting with Ha-rim, who poses to be Mr. Lee. While establishing a fake business with him, Won-ho learns his lines and eventually disguises just like Ha-rim, posing as Mr. Lee as Rak arranges a meeting between him and Park Sun-Chang, a criminal aspiring to work with Mr. Lee. Won-ho imitates Ha-rim and tricks Park Sun-Chang into believing he's Mr. Lee. But the tables turn when Park Sun-Chang offers him his own drug, and unable to refuse, Won-ho has to snort it. The drug shows its side effects but his team saves him. Won-ho and his team get the drug materials from Ha-rim and Rak takes them to two mute drug makers, Dong-Young and Joo-Young. As they produce drugs, a new criminal named Director Brian comes into play. Won-ho watches him from a distance and now having learnt of Rak's real identity from his own mouth as an adopted child of a family, he prepares to make the next move. Brian thrashes Sun-chang for meeting him in person, while Ha-rim's girlfriend Bo-Ryung arrives on spot as Won-ho and Rak are taking away the manufactured drugs, kidnapping them both. They are taken to Ha-rim and a prolonged fight ensues, resulting in Won-ho getting injured and Ha-rim getting killed by Rak, while one of the team members from Won-ho's team gets killed in an explosion at the drug manufacturing site. Bo-ryoung dies due to consuming the drug. Despite of being disappointed by their team member, Won-ho re-prepares his team to catch Brian, whom he suspects to be Mr. Lee. As they arrive at the site, Sun-chang takes Rak in a room, gagging to kill him. Fully convinced that Brian is not but posing to be Lee, Won-ho and his assistant officer break into a fight with Brian and his henchmen. Won-ho's team arrives to arrest the criminals, but as Rak kidnaps Brian, only to reveal himself to be the real Mr. Lee, he kills him with the help of his mute friends after making his condition similar to his dog. It is also revealed that Brian was the one responsible for the explosion causing the death of Rak's mother. An injured Won-ho searches for both Rak and Brian, only to find the latter severely wounded. He goes back to find Rak's dog missing. It is then revealed that Won-ho found out the dog's real name was Lieca, while trying to communicate with it. Rak had faked its name to be Jindo but had named their drug after his dog. Eventually, Won-ho tracks Rak down with the help of a GPS device he had planted on Lieca and finds him living with the mute drug makers. As Won-ho is fully aware that Rak is Mr. Lee, who is now officially declared dead, the latter offers him coffee as they both sit down to drink, with their guns on the table. Looking outside the window at the mountains, an emotional Won-ho asks Rak if he ever had been happy in his life, before the camera moves outside the house and a gunshot is heard.