Ten months have passed since the murder of Yan (Tony Leung) and Ming (Andy Lau) is now relegated to the admin section of the police department for secretarial duties while the investigation of the shooting continues. Of course, with Ming's previous history of flawless credits and a host of awards as a policeman, he gets away scott free and moves back into the office as head of Internal Affairs. But when several new cases involving high profile corrupt cops land on his desk, Ming immediately takes note. He is ordered to investigate the head of the Security Dept., Inspector Yeung (Leon Lai). Extremely ruthless, Yeung has risen well above Ming's ranks as a cop and also has ties to Sam, Yan, and a Godfather from China named Shen (Chen Daoming) who is known for drug trafficking and arms smuggling. But lately Yeung is linked to several "suicides" and other cop killings - all of which are later proved to be Sam's moles. Could Yeung be "the mole" of moles that Sam referred to previously? The man inside that Sam depends on more than Ming himself?