菲比（刘心悠 饰）的父亲阿九（廖启智 饰）在18年前因杀死合作的兄弟被对方遗孀洛华（林嘉欣 饰）追杀，菲比也成为了孤儿。幸好得到了领导人百德（曾志伟 饰）的照顾，收作养女，更扬言以后要娶菲比为妻，不让洛华对菲比作出进一步报复。

　　18年后的一天，就在百德打算退隐的时候，却遭到了别人的暗杀。于是，社团内的大风（黄秋生 饰）也想借此机会独揽大权。但百德临终前已经交托辰哥（任达华 饰）要协助菲比成为社团的最高领导，成为大家的“阿嫂”。

　　但社团里还是内藏暗涌，辰哥与花哥（方中信 饰）为菲比找来了保镖向东（刘烨 饰）。而这时江湖上也盛传杀死的百德的主使者是洛华及其助手（谢君豪 饰）。双方仇恨更加结深一层了……

In the macho triad world where heroes are molded from blood, brawn and brains, what place is there for a defenseless girl? The only exception to the rule is if you earn your respect as 'Ah Sou' - the big boss' wife. Ah Sou tells the extraordinary story of an innocent girl who becomes appointed successor to Hong Kong's ruling triad. This role becomes a double-edged sword for our young heroine, who is sucked into a maelstrom of vicious gang wars, hair-raising assassination attempts and ruthless power struggles and betrayals. Through numerous violent episodes and unexpected reversals, she discovers her own inner strength and re-writes the laws of the triad kingdom.

בחורה צעירה הופכת אל בוסית לשלישייה (אמא).

История невинной молодой девушки, которая попадает в водоворот порочных бандитских войн, убийств, безжалостной борьбы за власть и предательства.