In this gangster thriller the cops and the Triads have something in common: each has a mole in their midst. Ming (Andrew Lau) and Yan (Tony Leung) have been leading parallel lives: Ming is a Triad mole who has infiltrated the police department, and Yan is an undercover cop who has, over the years, risen to a position of authority in the Triad gang. Both are dissatisfied with their position, wishing they could put their false lives behind them. Then one night the two men's paths finally cross during a police raid. Both the police and the Triads realise they have informers amongst them, and the race begins for Ming and Yan to get out alive.