阿健是一名特警，近日力正在休病假。一天，早一场意外中，他就下了遭到了劫持的叶安娜（麦翠娴 饰），虽然做了一件好事，却因为打伤了三人已经人称“坏脑”的暴徒而遭到了停职处分。在另一宗珠宝抢劫案中，嫌疑犯老虎逃脱了恢恢法网，他和坏脑一拍即合，决定联手干一票大的，他们将目标放在了运钞车上。
一天，阿健带着叶安娜以及好友沙展文一起在逛街，对阿健一直心怀仇恨的坏脑开枪向三人射击，最终叶安娜身受重伤，沙展文则不幸死于非命。悲愤交加的阿健决定替好友报仇，他暗中调查觅得了老虎的处所，和陈帮办联手将这一窝蛇鼠端了个底朝天。

King-sized martial arts hero Sammo Hung stars in this wild and wacky blend of action and comedy. Skinny (Karl Maka) and Fatty (Sammo Hung) are a pair of police detectives who soon find themselves on the outs with their boss when they accidentally make a mess of his wedding while chasing Tak, a big league drug trafficker. Skinny and Fatty are forced to leave their jobs, but while on holiday in Singapore, they forget their troubles when they both find love with beautiful women. However, Tak is convinced the former cops are still a threat, and when he abducts their girlfriends, Skinny and Fatty swing into action to rescue them.

黑帮洪兴社与敌对帮派谈判破裂，双方大打出手。洪兴老大李坤混乱中被刺，重伤身亡，社团顿时一团混乱。留学并定居美国的李万豪（周润发 饰）携妻儿回港为父奔丧，在众老叔苦苦哀求下无奈出任龙头一职。虽生在黑社会家庭，但万豪自幼不参与社团事务，更对江湖上的规矩与利害一无所知，因此一系列改革举措招来了其他帮派的攻击与不满。
决意返美的万豪推举老成持重的谢胜（陈惠敏 饰）担当老大，此举却引来少壮派头目杨港（张耀扬 饰）的不满。内忧外患，处在过渡期的洪兴社风雨飘摇……