The young and beautiful Zuo Lan was originally a pure and kind girl with a boyfriend she had been in love with for many years. Because her father was addicted to gambling, Zuo Lan was humiliated in the process of debt collection. She thought her boyfriend would never leave her, but in order to get promoted, he sent Zuo Lan to the boss's bed, and Zuo Lan was heartbroken. The boss of Kowloon Walled City, Zui Ge, saved Zuo Lan who wanted to commit suicide. In order to avenge the people who ruined her life, Zuo Lan was determined to follow Zui Ge. In Zui Ge's repeated training, Zuo Lan killed the traitors of Kowloon Walled City and grew into a veritable sister-in-law of the underworld. After Zuo Lan took over the business of Kowloon Walled City, she designed to kill corrupt policemen and all those who had hurt her, and her revenge was avenged. Chen Jie, a subordinate who had followed Zui Ge for many years, had a crush on Zuo Lan. Seeing Zuo Lan's changes, he felt painful and wanted to persuade her to turn back. Zui Ge wanted to formally pass the throne to Zuo Lan on his deathbed, and told Chen Jie that he was a police undercover. At this moment, the Hong Kong Independent Commission Against Corruption has begun to clean up Kowloon Walled City. With external and internal troubles, how will Zuo Lan choose...