某社团老大乘车夜归途中遭人枪杀，凶手不知去向。该社团围绕继承人问题展开争论，为避免出现分裂与争执，社团元老马公（午马 饰）与王律师（黄霑 饰）商议，委托老大之名指定正直勤奋的阿修（李修贤 饰）为帮会继承人。
另一方面，与阿修同期的阿泰（陈观泰 饰）某日接到老大司机的电话，称阿修为刺杀老大的幕后指示。阿泰的小弟小奇（周星驰 饰）听到录音后恼羞成怒，发誓要阿修付出代价。一场裹挟了黑帮阴谋仇杀和兄弟情谊的战争随即展开…
Years ago in Hong Kong, Boss Cao (Zhao Lei)—the chairman of a company—was a former triad leader. Weary of the endless feuds and vendettas of the underworld, he decided to wash his hands of that life and retire. He also hoped his three adopted sons—Ah Xiu (Li Xiuxian), Ah Tai (Chen Guantai), and Ah Wei (Jiang Dawei)—would become law-abiding citizens. Upon his retirement, he secretly entrusted a will to his lawyer, instructing that it be made public in the event of his accidental death and that his business and assets be handed over to the specific son designated within the document.
A-Xiu, A-Wei, and A-Tai were once close brothers. Years ago, when A-Wei had to go on a business trip, he entrusted his girlfriend, Xing-Hui (Cally Kwong), to the care of A-Tai—who was introverted and steady in his ways. Seeing that A-Tai was poised to take over as the company's boss and moved by his constant care, Xing-Hui chose A-Tai and left A-Wei. Devastated upon his return and weary of the company's tedious affairs—as well as wanting no further part in the underworld—A-Wei moved to Hong Kong to run a fish farm, choosing to live a simple, ordinary life. Consequently, Boss Cao’s company came to be jointly managed by Ma Gong, A-Xiu, A-Tai, and others.
One evening, Boss Cao went to the cinema with his longtime close friends. After the movie, as they got into the car driven by his chauffeur, A-Biao, his friends—concerned for his safety—arranged for Xiao Qi (a subordinate of A-Tai) to provide an escort. Unexpectedly, A-Biao claimed the car was malfunctioning; he stepped out at a gas station to inspect it and used the opportunity to slip away. At that moment, a group of assassins launched an attack. Despite his friends' attempts to protect him, the assailants' firepower proved overwhelming, and Boss Cao, his friends, and their entourage were all killed. Xiao Qi, delayed by traffic, arrived a step too late to prevent the tragedy.
