In the 1960s, corruption was rampant in the Hong Kong police force, leading to many black prisons. Cheng An (played by Tony Leung), a reporter for Zheng Pao, wrote an article to expose the dark side of the police force, and was regarded as a thorn in the eye by Inspector Zhang Yaozu (played by Ng Yi-keung). Zhang Yaozu framed Cheng An for drug possession and put him in prison, and even defiled Cheng's girlfriend Xiaoci (played by Zhang Wenci). In prison, Cheng An was a "sheep" outside the gang members. Although he was looked after by the sheep's head airplane wood (played by Ng Man-tat), he was also insulted by the big guys. With his integrity and knowledge, Cheng An advocated for the rights of the prisoners, gradually gained the respect of the big guys, and his life in prison improved. Soon, the guard "No Humanity" (played by Lam Kwok-bun) killed the prisoner "Three Legs" (played by Elvis Tsui), and Cheng An used his friends in the newspaper industry to avenge Three Legs. Xiaoci relied on the power of another inspector to put Zhang Yaozu in prison. Zhang Yaozu, who became a prisoner, planned to retaliate against Cheng An in prison, and the confrontation between the two was inevitable...