Believer

When police officer Won Ho (Jo Jin Woong) loses his informant to a brutal murder, he becomes determined to track down the killer. He meets Oh Yeon Ok (Kim Sun Ryung), who reveals the mastermind is a mysterious drug cartel boss known as "Mr. Lee" - a dangerous criminal who carefully guards his identity and has previously attempted to kill her. Won Ho encounters Rak (Ryu Jun Yeol), a potential gang member, and convinces him to help set up a drug deal to expose Mr. Lee. However, the investigation becomes complicated when multiple criminals start using the "Mr. Lee" alias to conduct their own illegal operations. As Won Ho navigates this treacherous underworld, he must unravel the true identity of the country's most notorious drug lord. This is a 2018 South Korean crime thriller directed by Lee Hae Young, based on the 2012 film "Drug War."