In 1991, Hong Kong police inspector Wong Chi-shing meets his informant, Hon Sam. At the same time, Lau Kin-ming, Hon's prospective mole (espionage) within the Royal Hong Kong Police Force, assassinates Hon's triad (underground society) boss, Ngai Kwun. Lau is later greeted by Hon's wife, Mary, who casually ascertains whether he has any reservations about his mission for Hon. While giving him cash, Mary advises Lau to maintain a low profile. She also confesses that she was the person who ordered the hit on Ngai Kwun, admitting that Hon has no knowledge of this transgression and urges Lau to remain silent. Mary wants Hon to replace Ngai Kwun as the triad boss.