Lee Cheung-kong [Andy Lau] is an honorary soldier who is falsely accused of a robbery in China by his friends and is arrested by Officer Mo Heung-yeung [Elvis Tsui Kam-Kong]. His appeal is rejected and he is sentenced to death, but he stages a dramatic escape from execution, only to be stabbed by Mo during the chase. He illegally slips into Hong Kong, where he meets two illegal migrants, Seung Mun [Elizabeth Lee Mei-Fung] and Chicken Heart [Max Mok Siu-Chung], and a wary bond forms after she treats his wounds as they hide in a truck during a police sweep. Upon arriving in Hong Kong, Moon is sold into prostitution to repay debts, while Chicken Heart and his younger brother are taken in by triad boss Master Leung [Kirk Wong Chi-Keung] as labor. Cheung-kong owes HK$3,000 to Snakehead, the shipper of the illegal migrants, a debt his uncle refuses to acknowledge. Leung notices Cheung-kong's fighting skills when he confronts Snakehead and his henchmen, and offers to cover the debt and hire him at a construction site.
Leung learns about Moon's predicament and pushes Cheung-kong to join a jewel robbery gang led by Master Cheuk [Stephen Chan Tak-Gwong], and reveals to Cheung-kong the brothel where Moon is forced to work, but Leung tips off the brothel boss to anticipate Cheung-kong's arrival. Armed with a machete, Cheung-kong rescues Moon and fights off the brothel boss and his henchmen, but Moon is taken away in a car. Leung convinces Cheuk of Cheung-kong's fighting skills, so Cheuk arranges him to partner with Chicken Heart, whose brother was killed while taking a bullet for him. At this time, Mo is sent to Hong Kong to hunt for Cheung-kong. The Hong Kong police initially resist interference with the case, but the pursuit tightens as the operation progresses.
Cheuk leads Cheung-kong, Chicken Heart, and his gang to rob a jewelry shop where Cheung-kong shoots an off-duty police superintendent and Chicken Heart ends up trapped inside a safe with a manager. Cheung-kong breaks Chicken Heart out with a grenade and they flee from the police, while Cheuk refuses to release Moon, blaming Cheung-kong for the shooting and insisting on a new hiding place. Leung's underling, 966 [Lam Kai-Wing], guides Cheung-kong and Chicken Heart to a new hideout on a boat where Cheung-kong reunites with Moon.
Cheung-kong discovers Mo's arrival in Hong Kong to hunt for him and wants to leave, angering Cheuk, who orders his henchmen to capture Moon. Cheung-kong agrees to work for a full year for Cheuk so he can stay close to Moon, which Cheuk allows in exchange for his loyalty. Later, Leung is captured by Mo and beaten to reveal Cheung-kong's whereabouts, and the two factions maneuver Cheung-kong into a confrontation with Mo. Cheung-kong shoots at Mo, triggering a gunfight that ends with Cheung-kong subduing Mo but ultimately letting him go. Enraged, Cheuk threatens to sell Moon, and Cheung-kong fights both Cheuk and Leung, as Leung clears the way for him to contact Moon by phone and continue the ruse.
Meanwhile, Leung and Cheuk sexually assault Moon while she remains captive, a brutal turn that underscored the depth of betrayal surrounding the escape. During the next armored-truck heist, the crew realizes they were given blank guns by Leung and Cheuk. They force 966 to lead them to an apartment where Moon is hidden, and in the ensuing confrontation Cheung-kong fires a submachine gun, hurls Cheuk out the window, and escapes with Moon as the police converge. Chicken Heart dies on the way to the dock, while Moon sustains gunshot injuries. Mo arrives to stop Cheung-kong, but Kong insists they should seek medical help and promises to return when China’s laws allow it. In the end, Cheung-kong and Moon reach Panama and begin a new life together.
