TO and his wife LAM have been lurked and attacked by a mysterious man three times. They are frightened and they inform the police. When it is the second time for TO to go to the police station, LAM is killed in their house. Some background information of the couple has been collected. LAM is the foster daughter of a billionaire. After the rich man's death, LAM and the rich man's son CHI had an argument in the right to inherit the fortune. The court gave LAM the right and CHI hated LAM. CHI tries to hide where he was when LAM was killed but his lie is spoiled by the employee IVY. At last he has to admit that he was with a male prostitute when the crime was committed. It proves that he is innocent and the killer is someone else.

CHI attends LAM's funeral and there she recognizes that IVY is YUNG's ex-girlfriend. She also finds TO to be someone that she should know. Later CHI is killed in a traffic accident. The police discover that TO is not as loyal to his wife as one expects. Thus TO is believed to be the killer of LAM. YUNG leads his men to TO's office to arrest him. They cannot catch him because he dies after drinking a cup of poisonous coffee. Later it is found that IVY is TO's secret lover and her car is of the same model of colour of the one that killed CHI.

As the police has no other evident to accuse IVY, FUNG detentes her for forty-eight hours so as to collect more information. when YUNG sees YAN wearing the ring given by TO, he suspects her as the real secret lover of TO. His idea is consolidated when he sees YAN expressing her hatred by tearing LAM's clothes. Moreover YAN knows driving and she has a car similar to that of IVY. When they get the information of where the car is, YUNG and YI go to arrest the killer. They are late and the car has been driven away. However they do not give up. They follow it and at last pushes it into a dead-ended alley. There they check who the driver is.