Detective Hei (Leung), a kind-hearted veteran police officer and his partner Bong (Kaneshiro) bust a rapist in 2003. When Bong returns home after the bust, he finds his pregnant girlfriend has committed suicide. Since then, Bong becomes an alcoholic and turns in his badge to work as a private investigator. He is obsessed with finding out why his girlfriend committed suicide years ago.

Three years later, Bong discovers on the night of his girlfriend's suicide, she has been waiting at a bar for her secret lover, who wound up unconscious after a car accident the same night. Bong originally thinks that he will be angry at his girlfriend's lover, but he ends up taking care of the comatose lover while he lays in hospital. Bong eventually moves on and falls in love with a girl who sells beer in the same bar, Feng (Shu Qi).

Hei marries Susan (Xu Jinlei), daughter of billionaire Chau. Hei and two accomplices (two lowlifes) broke into Chau's home to rob and kill Chau and his butler Man. Later Hei killed his accomplices making it look like they killed each other in a dispute over the loot. Susan wasn't convinced about the two killers being alone, so she hired Hei's friend Bong to investigate further. As Bong got closer and closer to the truth, the story got more and more complicated. Ultimately, Bong discovered Hei murdered Chau for revenge. Chau had killed Hei's family when he was a boy living in Macau. Hei then took on a new identity. Hei also tried to kill his wife Susan to get her 300 million dollar inheritance, but she survived the attempt and went into a coma.

Although Hei's plan seemed flawless, he didn't account for himself falling passionately in love with Susan. When he visited Susan in hospital, he mentally confesses. Hei then realized that in his desire for vengeance for his family, he destroyed the new family that he created with Susan. Unable to bear the pain and anguish, he shoots himself in the head in front of his wife's dead body in the hospital.