刘国忠(任达华 饰)是一个身患绝症的警察,他的前途暗淡无光,他接到任务要保护一个证人的女儿。督察马军(甄子丹 饰)是身手了得的武术家,一心要接替忠的位置。忠派去黑道大哥宝爷(洪金宝 饰)身边的卧底意外死亡,原因不明,忠怀疑是宝爷所为。于是把宝爷押送到警局盘问,苦于没有证 据,忠迫不得已开始捏造证据控告宝爷,全警局都深谙此道,只有军蒙在鼓里。 然而,证据神秘消失,宝爷走出警局时,扬言要杀掉忠的所有手下,果然他身边的冷血杀手Jack(吴京 饰)干掉了忠一帮下属,马军意外发现,忠的下属和宝爷之间原来还另有恩怨,马军怒火中烧,决定与宝爷和Jack决一死战。A near retired inspector and his unit are willing to put down a crime boss at all costs while dealing with his replacement, who is getting in their way. Meanwhile, the crime boss sends his top henchmen to put an end to their dirty schemes.