[9] Won-ho is a police detective attempting to bring down Asia's biggest drug cartel run by a man called Mr. Lee.

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.

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.

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 severely wounds him with the help of his mute friends after making his condition similar to his dog.

Eventually, Won-ho tracks Rak down with the help of a GPS device he had planted on Laika 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.

The film's original ending leaves it unclear who has been shot, though the extended cut and 2023 sequel reveals it to be Rak.

[19] Richard Kuipers of Variety gave a positive review and wrote, "Believer may be more impressive around the edges than at its core, but that doesn’t prevent it from delivering a pretty solid two hours of action and suspense that’s muscularly directed by Lee and stylishly shot by Kim Tae-kyung.

"[20] Cary Darling of Houston Chronicle rated the film 3.5 out of 5 and said, "Lee Hae-yeong's gripping retelling of Johnnie To's Drug War...stands on its own and is different enough from the original to make it less a clone and more of a genuflection.

"[21] Simon Abrams of RogerEbert.com rated the film 2 out of 4 and said, "Believer doesn't add up to much because Lee and Chung essentially tried to improve something that was already perfectly unsettling.

[26][2] A sequel of the film, titled as Believer 2 has been confirmed by Netflix, which will be directed by Baek Jong-yul with the cast of Cho Jin-woong, Cha Seung-won, Han Hyo-joo, Oh Seung-hoon, Kim Dong-young, and Lee Joo-young.