In 1970s Hong Kong, rapacious landlords try to evict 72 tenants but sworn brothers Ha Kung and Shek Kin help the group of 72 defeat the landlord and landlady and coincidentally rescue Pinky from a planned forced marriage. When both sworn brothers fall for Pinky and propose to her, she flips a coin heads or tails, they both cheated during the toss but Ha wins her hand in marriage.

The sworn brothers become sworn enemies and Sheks hatred fuels intense rivalry against Ha in business dealings ranging from the manufacture of plastic flowers to the selling of stinky bean curd. Even after 40 years they continue to clash and in 2010 they are in keen competition selling electronics appliances in Sai Yeung Choi Street, Mongkok, the busiest street in the city and still home to the 72 tenants.

In fiercely competitive Sai Yeung Choi Street high rents force businessmen to use every means to survive, with electronics shops employing pseudo models in sales promotion campaigns and comic shops offering foot-massage services by Lolita, etc. These ploys are minor compared with the tactics of the landlord who threatens to close down the shops unless his demands for triple rental are met. Amidst this strife and struggle the street is hit by acid-attacks and in high spirits the 72 tenants unite and pledge to safeguard their home.

Against a background of fear and turmoil, with the old love triangle between Ha and Pinky and Shek still festering, the next generation of the Ha and Shek families embarks on their own heroic love affairs: MJ-style dancer Ha Junior is fascinated by Shek's daughter who is a Japanese AV culture fan; Ha's daughter, a kung fu maiden, is pursued by Shek's love-struck son, the smart shortie. Affairs of the heart yet to be resolved.