In a teahouse in Hong Kong, Royal Hong Kong Police inspectors “Tequila” Yuen and Benny Mak attempt to arrest a group of gun smugglers while they are making a deal. After an ambush from a rival gang member, a fierce gun battle breaks out. The gangsters are defeated but several police officers are badly wounded and Benny is killed. As revenge, Tequila executes the gangster who killed Benny rather than arrest him, much to the chagrin of his superintendent Pang, who needed the gangster alive to testify. Tequila is ordered off the case for his misdemeanor.
Elsewhere, Alan, an assassin under the employ of Triad boss “Uncle” Hoi, murders one of his subordinates who had double-crossed their clan for a rival syndicate led by upstart Johnny Wong. Wong, who is looking to usurp the old Triad bosses through his control of the illicit arms trade, is impressed by Alan’s skill and attempts to recruit him. Alan reluctantly accepts the offer. Wong brings Alan on a raid on Hoi’s warehouse, where many of Hoi’s men are killed. Hoi is outnumbered; he asks Alan to kill him but spare his men. Alan does so and shoots Hoi’s men as well. Tequila then attacks all of Wong’s men. During the chaos, Alan spares Tequila’s life.
Pang confirms to Tequila that Alan is an undercover cop. Tequila tracks Alan down to his sailboat to try to make sense of the situation, but the two are ambushed by the remnants of Hoi’s gang. Tequila and Alan manage to kill their attackers just before Wong arrives, which allows Alan to keep his cover. Wong realizes that one of his lieutenants, Foxy, is a police informant. Foxy is beaten at the docks by Wong’s henchman Mad Dog in front of Alan and Wong. Alan then shoots Foxy in the chest, although he secretly placed a cigarette lighter in Foxy’s breast pocket earlier to prevent the shot from being fatal. Foxy finds Tequila at a jazz bar and informs him that Wong’s armory is hidden in a vault beneath a nearby hospital. As Tequila takes Foxy to the hospital, Wong finds out that Foxy is alive and sends Alan to kill Foxy, as well as sending Mad Dog separately to cover Alan. At the hospital, Alan confronts Tequila, demanding to know the whereabouts of the vault. While the two are distracted, Foxy is killed by Mad Dog.
Alan and Tequila discover a hidden passage in the hospital leading to Wong’s vault. There, Mad Dog confronts them in a shootout. The police and gangsters arrive at the hospital. Wong has the patients and staff taken hostage. Over the night, many gangsters and police are shot by each other. Mad Dog requests the hostages be released, but Wong refuses. After fighting their way to the main lobby, Alan and Tequila liberate the kidnapped patients. Pang evacuates the lobby while officer Teresa Chang goes to the maternity ward to organize evacuating the babies. Alan and Tequila continue shooting gangsters, leading to Alan accidentally killing a cop. The duo eventually engage Mad Dog. While Tequila leaves to assist Chang with the babies, Alan and Mad Dog find themselves in a standoff with nurses and patients caught in the middle. They offer the group safe passage, but Wong shoots the group in a bid to kill Alan. For that, Mad Dog turns on Wong, but runs out of bullets. Wong kills Mad Dog while Alan escapes.
Tequila shoots gangsters while protecting the last baby in the hospital. Alan and Tequila are confronted by Wong, who sets off bombs to blow up the building. Alan refuses to escape, choosing to pursue Wong. Tequila jumps out of the hospital while holding wire cables, saving the baby while the hospital explodes. Wong drags Alan outside at gunpoint as a hostage. Wong has Tequila humiliate himself. Alan grabs Wong’s pistol and shoots himself through the stomach, giving Tequila the chance to shoot Wong dead.
To protect Alan from the triads, Pang and Tequila destroy Alan’s personnel file and declare him dead, allowing him to leave Hong Kong to find a new life.