“Don't cause trouble in the Walled City.”

In 1980s Hong Kong, troubled youth Chan Lok-kwun, a mainland refugee, struggles to survive in the Kowloon Walled City by joining underground fights. Betrayed by crime boss Mr. Big while trying to buy a fake ID, he steals drugs from him and seeks refuge in the Walled City, where he encounters Cyclone, a compassionate yet authoritative crime lord.