In Hong Kong during the late 1950s and early 1960s, there was police corruption and chaos everywhere. Among them, the Kowloon Walled City was an especially notorious place, where danger lurked and people were terrified. Idle youths Ah Hao (played by Lau Ching-Wan) and Ah Lok (played by Ng Ching-Fong) accidentally found themselves in this chaotic environment, getting swept up in the atmosphere of turmoil and enjoying their carefree life. They teamed up to gamble on horse racing, but this attracted the attention of the bookies who sought to harm them. Luckily, they were saved by the local gang leader, Fat Bao. Ah Hao then became Fat Bao’s disciple, and he struck up a bold romance with Fat Bao's younger sister, Ying (played by Peng Dan). He became daring and courageous, making a name for himself; Ah Lok became a police officer and married a girl named Fei Fei (played by Zhu Yin), with whom Ah Hao once had a fling. To provide a luxurious life for his vain wife, Ah Lok chose the path of corruption. These two brothers, one in the criminal underworld and the other in the police force, work hand in hand to carve out their own territory...