Set in the 1980s, troubled youth Chan Lok-kwun accidentally enters the Walled City, discovers the order amidst its chaos, and learns important life lessons along the way. In the Walled City, he becomes close friends with Shin, Twelfth Master and AV. Under the leadership of Tornado, they resist against the invasion of villain Mr. Big in a series of fierce battles. Together, they vow to protect the safe haven that is Kowloon Walled City.