Served as an undercover for several years, LEUNG SIU TONG or LAUGHING (Michael Tse) escaped from all calamity. Two years ago, he underwent special training, pretending to be mute and sneaked into an armed robbery gang as a spy. He successfullysolved the criminal case and later became an instructor for special training in undercover work. Unfortunately he was unable to adapt to the stress in the discipline, so he applied to be an undercover once again. His supervisor Chief Inspector CHOW MONG CHING (Fala Chen), looking exactly like his deceased girlfriend, was the person he communicates with during his undercover work. A female inspector and an undercover, falls into a black-white romance, and eventually became a pair that is in love, but cannot love.
Laughing wanted to get up top, so he went into the 'dark society firm' (triad) and got close to the leader SO SING PAK (Bosco Wong). Pak financially supported his childhood sweetheartYIU HO HO (Kate Tsui) so she can become a lawyer. Ho believed all along that she was deeply in love with Pak, hoping to break away from Pak and didn't want to work for him anymore. The two went through love, betrayal, separation and reunion. What two selfish people fears most is not knowing when they'll get betrayed again.
As an undercover, Laughing has no bottom line for anything he does. The highly intelligent and full of schemes, Pak goes on a battle of wits with Laughing. On the surface, they may seem like good brothers, but in factthey both have their own purpose, mutually taking advantage of one another.