帮帮（黄子华 饰）是屯门的“土著”，长这么大了他还从来没有离开过屯门，对外面的世界充满恐惧。帮帮一直寄居在姐姐家里，整日游手好闲、不务正业，期望有朝一日能找到一条发财妙计。一日，帮帮遇上了丑女士碌架（郭羡妮 饰），对她产生了好感，于是决心为了她而改变；而士碌架因为帮帮的侧面极像她已经离世的父亲，对他亦心生好感。两人越走越近。

　　一次帮帮偶然发现了一个色魔在企图侮辱一名少女，惊慌之下大喊救命经色魔吓跑救回了少女。一个发财妙计在帮帮的脑中产生，那就是每次收取独自回家的少女8到10元不等，充当她们的临时保镖。在士碌架的渲染下，“屯门有色魔”这件事很快传遍了街坊，一时间人人人自危，于是帮帮的生意开始火爆起来。眼看发财在即，两人都十分开心，可是，好景不长…

Bon Bon, a resident of Tuen Mun, who's always attempting to implement his latest pyramid scheme. Bon Bon saves daffy local girl Snooker from a potential rapist and decides to implement his latest scheme, "One Dollar Bodyguard": he'll protect women on their evening strolls for one HK dollar. Bon Bon has to attend to his own problem, which is his inability to ride in a moving vehicle, that strands him in Tuen Mun for life. And there's the romantic issue with Snooker to resolve.