Plot Summary: It's about a cop named Yan (played by Tony Leung) going deep undercover into the Triads, and Triad member Ming (Andy Lau), who infiltrates the police department. Each mole was planted by the rival organization to gain an advantage in intelligence over the other side. When they got more involved in their new undercover lives, they had more to cope with. The film begins with a deal between Sam (Eric Tsang) and a Thai cocaine dealer that is interrupted by Police Superintendent Wong (Anthony Wong) and his team. This is thanks to Yan passing on important information to Wong but unfortunately, it also reveals to Wong and Sam that they each have moles within their respective organizations (with Ming alerting Sam in the nick of time, Sam ordered his minions to dispose of the cocaine so that the police didn't have any real evidence on their hands). Now, both Yan and Ming are in a race against time to root out the other mole.
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