Big F, who’s just gotten out of prison, wastes no time in tracking down his old comrades, picking up bowling alley employee Crazy B, back-alley hairstylist Johnny T and mechanic East L in quick succession. As it turns out, Big F wants to rob a truck transporting dirty money across the Mainland-Hong Kong border, and to do that, the gang’s got to pose as police officers. On the day of the heist, the men set off in their minibus-turned-police-vehicle dressed as cops and armed with BB guns. What they don’t know is that another group of criminals also has its sights set on the truck and those people have AK-47s.
捱过了十六年的铁窗生涯，义气冠绝黑道的发哥（吴镇宇 饰）出狱后，第一时间实行他那苦思多年的惊天妙计：召集昔日好兄弟，如熟悉一切机械的保龄球场维修员丧宝（任达华 饰），潦倒后巷造型师杜公子（谭耀文 饰）、以及昔日辣手车神现任小巴司机林东（郑浩南 饰），合力将一架十六座小巴改装成冲锋车，用最“和平”的方式，打劫一辆走私黑钱的运尸车。计划看似天衣无缝，但仍逃不过警员徐安良（古巨基 饰）的法眼。凭着过人的观察力和直觉，他洞悉了发哥等人的大计；虽然未有警方的正式任命，他仍私下追捕这帮“装警察”的抢劫集团……偏偏这个时候杀出另一班心狠手辣的悍匪（姜皓文、思漩 饰），目标同样是运尸车。当真悍匪vs假警员，真贼车vs假警车，教发哥一众兄弟如何收场？再加上途经的无辜一家三口、一架雪糕车、一个疯疯癫癫的阿婆、 以及专门养殖蟑螂的怪人，在那夜凌晨，展开连场疯狂追逐战……