罗姓富豪笃信命理之说，为保财运使正室与女仆分别怀孕，日后两名儿子同时出生，高姓大师判定两子为旺财星跟灾星转世……一晃多年，香港街头又多了一名潦倒青年罗四两（张家辉 饰），四两封赌必胜，但却会给亲人带来灾运，自从三岁时克死生父，便由三叔抚养成人，身边只有青梅竹马的好友阿花（杨恭如 饰）不时照顾搭救。而四两同父异母的兄弟司徒定一（杜德伟 饰）却在高师傅维护之下财运亨通，更兼赌术超人轻松羞辱赌王李大胜。定一为保持好运将四两控制在手中二十余年，直至四两被李大胜关入赌术研究中心。四两在中心结识一“外星遗孤”（李灿森 饰）并终于发现自己其实一直生活在假象之中。面临人生大难的定一为转运设计陷害四两，兄弟之战在所难免……

豪商羅老爺正室產子，產房燈火通明、服侍周到，兒子取名羅定一。另一方面下人司徒阿綺，因受羅老爺污辱，因奸成孕，於同日在潮濕邋遢的幽暗廚房內獨自產子，取名羅四兩。及後兩母子更被羅老爺趕出家門。四兩與方天鐸最後與司徒定一決戰一局，以生命作賭注，決定大家今後命運，決定「賭俠」誰屬

Two brothers, Yat and Leung, with different mothers have different fates. After Leung and his mother being expelled from the family, they are housed by a feng shui master. Leung is a lucky guy and brings a good fortune to his mother. On the other side, Yat's presence poses a tragic threat to his family. Eventually, Yat's parents die and Leung's mother decides to raise Yat and the two boys exchange their names. However, their lives will turn upside down when they reach the age of thirty. The only way Yat can retain his luck is to overtake all the good luck from Leung.