The plot mostly involves the two main characters, Ching and Yiu and problems they face with Mickey, a fellow inmate and "Killer", a prison guard. Yiu is sentenced to three years for manslaughter. In a fight for his father, he pushed a man that was then run over by a bus.
Ching was sent to prison for killing his wife for being a prostitute.
During the end of the film, inmates decide to go on hunger strike to protest against the cigarette price rise, this causes problems with Assassin.
Ching bit Killer's ear off and gets an extended sentence, continued on Prison on Fire II, Yiu is released later on.