In Hong Kong, triad power is on display as Uncle Eight Taels, Wong Kau-Tai, lies terminally ill and calls his son to take the helm before he dies. His brother, 7.5 Taels, and his loyal bodyguard Chung wait for Wong’s arrival, hoping the family leadership will stay intact.
Yip Sin-man is a grown man with the mentality of a five-year-old who is taken by two members of the Ministry of Foreign Affairs from China to India to study. Despite his condition, Yip proves to be a fast learner. At the Indian airport, Wong Kau-tai is also present, but is arrested for breaking a telephone. In a chaotic turn, Wong drops his passport and an Indian kid picks it up, handing it to Yip and inadvertently sending him back to Hong Kong with the two ministers left behind.
Back in Hong Kong, Chung retrieves Yip at the airport and refers to him as “Big Brother,” a label Yip does not fully comprehend. The situation grows tense when Hau-tin, a triad member intent on killing Yip to seize control, confronts Yip at his home, only to witness Yip’s clumsy yet endearing request to tie Hau-tin’s shoes. Fearing for Yip’s safety, Chung teaches him how to handle guns—though Yip shows little interest in weaponry—as the bodyguards shadow him, while Yip simply wants to buy toys and play.
The next day, Yip and his entourage head to a toy store where Yip spots a motorcycle. The shop manager refuses to sell it, and later, [7.5 Taels]’s henchmen threaten the shop into compliance. Yip then goes to the police station and meets Superintendent Lam. Yip agrees to help Lam by urging his underlings to participate in an “Anti-Violence Movement.” Back home, Yip disciplines his underlings with playful punishments—clip, glue, and a spanking—sparking lighthearted humor about whether such methods suit triads. Meanwhile, Hau-tin is ordered away from drug trafficking and told to sell cigarettes instead.
During this time, Chi-lam, the daughter of rival gang leader Master Dragon, plots to kill Yip to aid her father’s power. That very night, Yip and Chi-lam meet and, in a spark of instant attraction, fall in love. Their connection deepens quickly, and the next day they marry. Yet Chi-lam’s plan to kill Yip lingers, and at night she moves toward murder until a large portrait of her in Yip’s bedroom makes her pause and hesitate. Still, she remains torn, and Yip senses that she might not be Wong Kau-tai after all.
Chi-lam’s sister eventually reveals the truth about Yip’s identity and shows her a photo of an Italian mob boss who supposedly knows Wong Kau-tai in Hong Kong. To preserve Yip’s ruse, Chi-lam ends up killing the mob boss at a bar, a move that draws Hau-tin to inform the police and leads to Chi-lam’s arrest at Yip’s mansion. The shock reveals to everyone that Yip is not Wong Kau-tai, prompting his departure with [7.5 Taels] and his daughter, Sandra Ng Kwan Yue.
On a desolate road, their car stalls and Chung returns, this time to kill Yip under orders from Kau-man Lung. Chung aims a gun at Yip in a tense standoff, but Yip empties the bullets. As the countdown—1, 2, 3—reaches its end, [7.5 Taels] shoots Chung with his own gun. It later becomes clear that Chung’s gun was empty on purpose, a staging device to set up Hau-tin as the next target. Chi-lam’s sister, Vindy Chan Wai-Yee, arrives to whisk them away to the mansion.
Back at the mansion, Hau-tin makes a last, brutal attempt to force himself on Chi-lam just as Yip returns. [7.5 Taels] arrives with three guns, trying to shoot Hau-tin and his henchmen, but the defense holds and a fierce gunbattle erupts. One by one, Hau-tin’s men fall. Hau-tin gains the upper hand over Yip, Chi-lam, and 7.5 Taels when bullets run dry, and an injured Chung limps in to disrupt Hau-tin’s momentum by disabling Hau-tin’s gun. Seizing the moment, Yip confronts Hau-tin, and after a tense struggle, he delivers the final blow, ending Hau-tin’s violent threat, a moment that underscores Yip’s reluctant but decisive resolve to protect those he loves.
