Lung joi bin yuen (1999)

Five years ago, Shing, an outstanding trainee at the police academy, was hand-picked to go under cover in the Hung Hing triad. There, he became close friends with their toughest leader Fei Lung. When territorial war breaks out between Fei Lung's buddy Leopard and a rival gang led by Tall Guy, Shing comes into contact with White Head, another undercover cop. Soon, Shing is caught between the need to protect White Head, and his loyalty toward Fei Lung.