纵横江湖二十年的黑帮大佬任因久（梁家辉）因行事夸张不择手段，树敌无数。其潜在警方中做卧底的手下叶伟信（陈奕迅）某次查案时，得知有人要置他于死地放风给他，不想被他当作无聊笑话摇头摆手。直到某次正在理发时一颗从暗处飞来的子弹在他头发上留下焦坑，任因久才相信的确有人要取他性命，即刻以“江湖告急”的戏言，传令召开江湖大会。而叶伟信接手调查后，提醒任因久以古龙笔下的名句“最大的敌人永远是你身边的朋友”来将嫌疑人列表，结果老婆苏花（吴君如）第一个出现在任因久脑海。

Gang leader Jim Yam has ascended nearly to the pinnacle of power in the underworld, but it brings him few satisfactions. As he watches his peers drop dead around him - many of them amazingly from natural causes - he finds himself more and more soldiering on because that's just what bosses do. Reflecting back on his younger days in London, it is sad to contrast his current lavish - but empty - life as a crime lord in Hong Kong with the joys he experienced as a petty thief in England. These flashbacks and voice overs give us insights not only into Yam himself, but also his closest associates, whom we discover he in truth barely knows.

Chef de triade vieillissant, Jim Yam a passé toute son existence à affirmer son emprise sur le quartier de Jiang Hu. Mais sa vie bascule lorsqu'il apprend qu'un contrat a été placé sur sa tête. Devenu la cible d'un tueur mystérieux, Jim Yam n'a que quelques heures pour déjouer le complot et découvrir qui veut sa mort. Dès lors, il va se méfier de tout et de tous.