A girl named Ha Yoon-joo joins a police division where the members are largely unarmed and don't wear uniforms. Led by a man named Hwang, the division avoids arresting criminals and focuses exclusively on following them around to gather information. One day a bank is robbed and only one of the seven criminals is caught on camera. In response, Hwang, Ha, and six other officers spend several weeks wandering around the city streets, tagging after people who match the criminal's physical description. When they finally find him, they put cameras outside his apartment.
Meanwhile, James, the leader of the criminals, wishes to quit his line of work, but his elderly mentor responds by sending a man to kill him, whom he successfully defends against. When James's subordinates confer to discuss the next mission, they are successfully tracked by Hwang's officers, who call in a SWAT team to subdue them. James, who was standing in a separate location, finds it necessary to murder one of Hwang's officers to escape. Later, after James is given criticism from the mentor, he attacks the mentor's hide-out, murdering the mentor and his body-guards. He then acquires a fake Thai pass-port and gets ready to leave South Korea.
Hwang and Ha both feel sad at the death of their colleague. As a result, Hwang announces his resignation while Ha takes a leave of absence. However, while Ha is doing her laundry, she suddenly remembers using her photographic memory that she has run into James in the past. Namely, on the day of her police interview, James had fleetingly walked past her inside a subway car, carrying a grocery store brochure. Ha runs to the grocery store and waits there, managing to catch sight of James again, and urgently notifies Hwang and his officers while staying on James's tail. When James walks into a tunnel, Hwang takes over the pursuit, but James recognizes Hwang and stabs him. Luckily, though, the wound isn't mortal. Ha continues the pursuit into the subway tunnels but is also recognized by James and held hostage. When the SWAT team comes, James lets go of Ha and runs deeper into the tunnels.
As the chase goes on, James finds himself trapped between an advancing SWAT team and the mouth of the tunnel, which is being guarded by Hwang, who ran the long way around. As James decides to charge at Hwang, the latter, finding himself at the juncture of an oncoming train, stands his ground to shoot at James, risking a 50/50 chance that the train will flatten him. Fortunately, the train takes the other branch and James is hit by Hwang's revolver and killed. Encouraged by the success, Hwang withdraws his resignation, and together with Ha, goes on to execute further such missions including the pursuit of international terrorists.
