Kung and Kin's rivalry goes way back to the seventies when they fought over the same girl, who eventually became Kung's wife. Now they run competing phone stores right across from each other on Mongkok's busiest street, and stretch their minds trying to outdo each other with crazy promotions.

Laughing is formally a police undercover. However due to a drug trafficking case, Inspector Pan is hot on his trails. Before Laughing becomes a police undercover, he works under triad leader Yi. Yi treats Laughing as his own brother, however to protect his territory and illegal businesses, Yi instructed Laughing to join the police force and act as his undercover. Laughing is a high-flyer in the police academy. However he never got a chance to join the force because he is specially picked by Inspector Xian to be an undercover in the underworld syndicate. Hence Laughing becomes a “double-undercover”. Yi is happy that Laughing is allocated to the triad of his rival. To make his situation worse, Laughing falls in love with the triad leader’s sister, Karen. Justice, brotherhood and love, what will Laughing decide on? His decision will be a turning point in his life.