Kim Hyuk (Joo Jin-mo) is a detective in the South Korean National Police Agency, having escaped from North Korea as a teenager. Unbeknownst to his superiors, he also works as an illegal arms smuggler with his best friend and partner in crime, Lee Young-choon (Song Seung-heon), who also defected from the North.
Hyuk has a younger brother, Chul (Kim Kang-woo), whom he was forced to leave behind (along with their mother) during his escape. Guilt-ridden over leaving his brother behind, Hyuk has spent the past few years searching for his brother. Eventually, he finds Chul in an internment camp but Chul resents Hyuk for leaving behind the family to escape. It is then revealed that their mother was killed sometime after Hyuk’s escape.
Hyuk goes to Thailand to complete an arms deal, accompanied by Jung Tae-min (Jo Han-sun), a new member of the smuggling operation. However they were double-crossed by Jung and the Thai gang. Jung escapes, while Hyuk is captured and sentenced to prison for three years. After reading about Hyuk’s capture in the newspaper, Lee finds the Thai gangster in a massage parlor and kills him and his henchmen. However, in the ensuing gunfight, he is shot in the knee and crippled.
After Hyuk is released from custody. Remorseful and determined to start a new life, he finds work as a taxi driver. Meanwhile, Chul has become an officer in the National Police and Jung has become the leader of the arms smuggling operation, while Lee does odd jobs to survive. During an emotional reunion, Lee asks Hyuk to return to the underworld to take revenge on Jung, but Hyuk refuses.
Hyuk seeks Chul out, hoping for a reconciliation, but Chul rebuffs him, seeing Hyuk as nothing but a criminal and still resentful that Hyuk left the family in North Korea. Jung finds Hyuk and presses him to rejoin the organization, offering to bring Young-choon along if Hyuk rejoins, but Hyuk refuses. Meanwhile, Chul is obsessed with arresting Jung and bringing down the arms operation. After Jung has Young-choon beaten and threatens to harm Chul, Hyuk decides to join Young-choon in taking revenge on Jung. Hyuk and Young-choon steal incriminating evidence from the smuggling business and use it to ransom Jung in exchange for money and an escape boat. However, Hyuk has given the evidence to the police. Using Jung as a hostage, Hyuk and Young-choon take the money to a pier, intending to escape in the boat. Meanwhile, having followed his brother, Chul arrives on the scene but is captured by Jung’s men. Even though he is free to escape, Hyuk decides to return to save Chul and asks Young-choon to leave on his own.
Hyuk returns and offers to exchange Jung for Chul, but the trade explodes into a wild shootout. Hyuk and Chul are wounded and pinned down, but saved by Young-choon, who turned the boat around out of loyalty to Hyuk. After killing many of Jung’s men, Young-choon berates Chul, telling him that he should be grateful to have a brother like Hyuk. Young-choon is in turn gunned down by Jung’s men. The police arrive and begin arresting Jung’s men. Jung evades capture and escapes into a steelyard. Hyuk and Chul chase after him, but Hyuk is shot and killed when he shields Chul from Jung’s gunfire. Jung mocks Chul and prepares to surrender to the surrounding police. Despite warnings from the police to drop his weapon, Chul shoots and kills Jung. As the police advance, Chul cradles his brother’s body in his arms and tearfully laments that he missed him. He aims his gun to his head and the scene cuts to black as a single gunshot is heard.