Operation Boar Hunt, the Royal Hong Kong Police Force’s undercover sting to arrest crime lord Chu Tao, kicks off with officers tucked away in a shantytown. The plan hits a snag when the criminals spot the approach, and a tense shootout erupts, sending civilians scrambling and framing a chaotic crossfire. Chu Tao and his men shove their car through the town, crash downhill, and hop out to vanish on foot. Undercover officer Sergeant Chan Ka-Kui [Jackie Chan] guides the pursuit on foot as Tao and his crew try to bolt in a double-decker bus, and Ka-Kui stops the vehicle by leveling his service revolver at the driver, a decision that underscores the danger of every move.
Back at the station, Chief Inspector Raymond Li [Lam Kwok-Hung] chastises Ka-Kui for letting the operation spiral, but the brass later projects him as a model officer to appease higher-ups. Ka-Kui’s next assignment is to shield Chu Tao’s secretary Salina Fong [Brigitte Lin], who is pressured to testify about Chu Tao’s criminal activities. Salina resists at first, but a fellow officer stages a break-in with a knife-wielding assailant, and after a rough confrontation she agrees to cooperate. They drive away in Salina’s car, only to be ambushed by Tao’s real hitmen; Salina frightens them off by brandishing Ka-Kui’s revolver, forcing the attackers to flee.
When Ka-Kui returns to his apartment, he finds his girlfriend May [Maggie Cheung] and her friends throwing him a birthday party. May grows angry at the sight of Salina wearing lingerie and Ka-Kui’s jacket, misreading the situation until Ka-Kui explains that Salina is a witness. The tension deepens as Salina discovers that the apartment assault was a sham and decides to record over her confession about working for Chu Tao. She slips away while Ka-Kui sleeps, and she is not present at the next day’s trial, which collapses due to her absence and the tampered recording.
Even with Chu Tao released on bail, his vendetta intensifies. He captures Salina to force silence, but Ka-Kui locates and frees her, only to be assaulted by Tao’s men. Inspector Man reveals that he has been colluding with Chu Tao, turning Salina’s capture into a ruse designed to trap Ka-Kui. The plan escalates toward a setup where Tao’s henchmen would kill Ka-Kui with Ka-Kui’s own gun to frame him for murder. Now a fugitive in the eyes of the law, Ka-Kui returns to the police station to plead his case, but the Chief Inspector orders his arrest. In a desperate move, Ka-Kui seizes the Chief Inspector as a hostage to escape, then releases his cooperative superior to continue the investigation.
Salina heads to Chu Tao’s mall office to download incriminating data from the computer system. Tao learns of the breach and rushes to the mall with his men, while Ka-Kui and May tail them. In the ensuing carnage, Ka-Kui defeats Tao’s henchmen and tears through the mall, sending displays and fixtures flying as the conflict spills onto multiple floors. The data-bearing briefcase lands on the lower level, only to be reclaimed by Tao and his crew after they strike May. On the top floor, Ka-Kui slides down a pole wrapped in light bulbs to the bottom and corners Tao. Reinforcements arrive just in time to keep him from taking matters entirely into his own hands. Salina testifies that Tao ordered Inspector Man killed and that the crucial evidence is inside the briefcase. Tao’s defense attorney accuses the police of misconduct, provoking Ka-Kui to unleash a fierce beating before his friends intervene.
