Cheung Ka-wah Andy Lau and his older brother Ka-wai David Lam Wai try to reach Hong Kong illegally with their parents aboard a refugee ship. As they near the Chinese coast, tragedy strikes: their sick mother suffocates on the deck, and a firefight erupts between the refugees and approaching coast guards, during which their father is killed. Ka-wah grabs a pistol, fights back, and leaps into the sea, managing to slip into Hong Kong and is rescued by a boat girl named Kiu Irene Wan and her grandfather, who nurture him back to health. Meanwhile Ka-wai is captured and deported to mainland China, where he’s forced to work in a mine quarry.
Back in Hong Kong, Ka-wai struggles to find steady work, and when he eventually sets up a Red bean ice stall in Sai Wan, he’s confronted by triad thugs trying to extort protection money. He stands his ground, and in the ensuing trouble his stall is wrecked. The confrontation brings him to the Wan Lai Tea Room, where he interrupts Tong Fai Michael Chan Wai-Man as he gambles against his rival Fat Hoi Shum Wai in a bird fight. Ka-wah storms in, tears apart Fai’s bird cage, and assaults several henchmen. Outnumbered, he seems doomed until Fai, recognizing Ka-wah’s courage and fighting spirit, takes him under his wing and treats him like a son.
The criminal underworld shifts as Fat Hoi convinces his boss to push cocaine trafficking, a plan Fai opposes. The boss agrees, but Fat Hoi retaliates by hiring outside thugs from Sheung Wan to disrupt Ka-wah and Kiu’s wedding. When the boss learns of Fat Hoi’s overreach, he punishes Fat Hoi, who retaliates by framing Fai for cocaine possession—sending Fai to prison for seven years. Fai urges Ka-wah to put distance between them to stay safe, so Ka-wah moves to Keelung, Taiwan with Kiu, adopting the name Cheung Tin-chau and taking a job at a shipping company owned by Kiu’s uncle. With Fai behind bars, Fat Hoi’s operation expands and he eventually aligns with Thai drug lords to push even bigger profits.
Seven years pass. Ka-wah has started a family, fathering a daughter named San-san with Kiu, who is pregnant with their second child. He eventually takes over the shipping company from Kiu’s ailing uncle, while Fat Hoi rises to leadership of the Chung Sing Tong Gang and runs a transport business that traffics cocaine. So, an adviser within Fat Hoi’s circle, pushes the idea of investing in legitimate ventures as the British government begins to crack down on corruption. To fund his expansion, Fat Hoi hires mainland criminals to rob an armored car—a job that includes Ka-wai among the participants.
Fat Hoi’s Thai partner then proposes smuggling HK$10 million worth of cocaine to Taiwan and invites Ka-wah to join the venture; Ka-wah refuses. Fat Hoi travels to Keelung to pressure him, and Ka-wah warns Fat Hoi’s crew to depart Taiwan within 24 hours. In retaliation, Fat Hoi orders Ka-wai to kidnap Ka-wah’s daughter San-san, but the attempt ends in tragedy when Ka-wai accidentally suffocates the child, leaving Ka-wah to grapple with guilt and a deepening sense of vengeance.
Back in Hong Kong, Ka-wah discovers Fai now works as a window washer for Fat Hoi and has fallen into cocaine addiction, driven by coercion from Fai’s prison years. Ka-wah resolves to help Fai kick the habit, but Fat Hoi responds with brutal force: Ka-wai and a Vietnamese henchman are sent to kill Ka-wah at Fai’s hideout, where Fai is killed by the Vietnamese assailant. Ka-wai, witnessing the chaos, kills the Vietnamese killer and returns with Ka-wah to the hotel room. There, Kiu—who has learned of her daughter’s abduction and witnessed Ka-wai’s role in it—confronts Ka-wai, and guilt tears at him as he realizes the burden of his past deeds.
Ka-wah briefly consoles Kiu and steels himself for revenge. The trio infiltrates Fat Hoi’s banquet, where Ka-wah moves with deadly precision: he slaughters Fat Hoi’s henchmen with a hand saw, enabling Ka-wai to free and support Kiu as they join Ka-wah in exacting justice. When the police finally arrive, Ka-wai makes a final choice to push his brother aside, but Fat Hoi is fatally wounded by gunfire as the law closes in, leaving the two brothers to confront the consequences of a violent life and the cost of loyalty, family, and vengeance.
