Cheng Chao-an Bruce Lee is a Chinese mainlander who moves to Pak Chong, Thailand to live with his extended family and to work in an ice factory. He meets his cousin Hsu Chien James Tien Chun when Hsu stands up to local street thugs who beat his kid brother. Cheng refrains from getting involved despite being tempted to, because he had sworn to his mother never to participate in any fighting, and wears a jade amulet as a reminder of his pledge.
Cheng begins his work at the factory. When an ice block is accidentally broken, a bag of white powder — obviously illegal drugs — falls out. Two of Cheng's cousins pick up the bag and are told to see the manager later that night, who tell them that the factory is a front for a drug smuggling ring led by Hsiao Mi (the Big Boss) Han Ying-Chieh. The discovery unsettles everyone, and the tension thickens as the workers try to make sense of the danger surrounding them. When Cheng's cousins (Wang and Chang) refuse to join them, the manager sends his thugs to kill them and dispose of their bodies, thereby preserving the secret.
Hsu Chien and Ah Pi Billy Chan Wui-Ngai go to Hsiao Mi's mansion to find out what happened to the Wang and Chang. Hsu doubts Hsiao's claims that he knows nothing and threatens to go to the authorities, leading the boss to set his gang on the duo. After a brutal battle, they are also killed. When the Chinese workers at the factory learn that Hsu and Ah Pi are missing, they refuse to work and start a riot against the Thai management, who are joined by a group of hired thugs.
Cheng still refuses to participate, but during the chaos, one of the thugs accidentally rips off and breaks Cheng's amulet. Enraged, Cheng jumps into the brawl and beats the thugs, causing them to flee. To reduce tensions, the factory manager makes Cheng a foreman, inviting him to a dinner that night to meet the boss. Everyone is happy that Cheng is the new foreman, except Chow Mei [Maria Yi], because the others have forgotten about the missing men. Cheng promises to find out what he can about them.
At the dinner, the manager tells Cheng that the boss cannot make it due to a meeting with visitors from out of town. Several women arrive at the dinner table, sit next to Cheng, and ply him with cognac. Cheng gets drunk and spends the night with Sun Wu Man [Marilyn Bautista], a prostitute who attended the dinner. Cheng meets Chow Mei as he leaves the brothel in the morning, embarrassing him.
Because Cheng attended the dinner and got drunk, he did not follow up on his promise to speak to the police about the missing men. He tells his family when he returns home that he forgot. This causes much unease for Cheng's family and friends, who believe that Cheng is reveling in his new position instead of helping to look for their brothers. They resent him, except Chow Mei, who stands up for him.
Later, Sun Wu Man warns Cheng that his life is in danger and reveals that Hsiao Mi is running a drug trafficking operation. Immediately after Cheng leaves, Hsiao's son, Hsiao Chiun Tony Liu, sneaks in and murders Sun Wu Man. Cheng breaks into the factory and first finds the drugs before discovering a hand, the head of Sun Wu Man, and the head of Hsu Chien James Tien Chun in the ice blocks. Cheng is surrounded by Hsiao Chiun and a group of his men. Cheng fights his way out, killing Hsiao Chiun and his gang in the process. He returns home to find that his remaining family members have been murdered, while Chow Mei is missing. Mourning his loss by a river, Cheng vows to exact revenge, even if he dies.
Cheng subsequently storms Hsiao Mi's mansion to fight him and his men. One of Hsiao Mi's disgruntled slaves frees Chow Mei, who was being held hostage in a cramped room used as a prison cell. She runs away to get help from the Thai police. Cheng finally kills Hsiao Mi after a fierce fight by deflecting the knife Mi throws at him with his shoe. Once he learns that Chow Mei is safe (as she came running along with the police division), he surrenders to the police when they arrive at the mansion.
