The narrative upends undercover conventions early when Hyun-soo voluntarily reveals to Jae-ho in prison that he is an undercover police detective targeting Chairman Ko's syndicate, forming a bond built on this confession. When Hyun-soo's mother dies in a hit-and-run, Chief Chun refuses him funeral leave, whereas Jae-ho arranges and funds his attendance, earning Hyun-soo's total loyalty. However, it is later revealed that Jae-ho orchestrated the hit-and-run murder of Hyun-soo's mother to make Hyun-soo entirely dependent on him.
Chief Chun provides Hyun-soo with CCTV evidence of the murder to turn him against Jae-ho. Meanwhile, Jae-ho assassinates Chairman Ko to seize control of the syndicate and kills Byung-gab to protect Hyun-soo. Hyun-soo sets a police ambush for Jae-ho, but Jae-ho wipes out the squad and runs over Chief Chun. In the climactic confrontation, Jae-ho points a gun at Hyun-soo but lowers his weapon out of love. Hyun-soo tackles and suffocates Jae-ho to death, with Jae-ho whispering his final warning: "Don't you ever make a mistake like mine [trusting you]".
Hyun-soo subsequently executes the wounded Chief Chun with her own gun, frames Jae-ho by planting the weapon on his body, and lies down inside Jae-ho's red sports car. The film concludes with an overhead shot of Hyun-soo staring into the sky in an empty, spiritually shattered stupor.