YUNG and CHIT determine their date of marriage. In order to be a good wife, CHIT attends a cooking course. In the education centre, she meets a mysterious lady who intends to attend all courses. CHIT finds a vague image of the lady in her mind. She remembers that the lady is called TUEN MUK CHI. There was a lady with the same name who committed suicide six months ago. YUNG checks the file again and learns that the victim had left a letter to CHRIS before she killed herself. According to the record, CHI lived in CHING’s house. CHING is attacked and her house has been searched. CHIT suspects that CHRIS is NAM who works as a tutor in the education centre. However NAM is killed with a knife in the show room.

The killer leaves no clue in the show room. After investigation, it is found that CHI is the daughter of WANG who runs big rubber business in Malaysia. As WANG did not accept CHI's boyfriend, CHI eloped with her boyfriend to Hong Kong. Some information of CHING and her photograph are found in NAM's house. It is because NAM has hired a private detective to check her. An employee of the education centre reports that before NAM was killed, he had had secret discussion with another tutor YUEN. Later YUEN is found killed by poison. Incidentally YUNG gets a video tape from a peeping Tom. From it the secret relationship between CHI, YUEN and NAM is exposed. They suspect that the killer is one of those in the education centre.

The real identity of SUN, who works as the school janitor in the education centre, is confirmed. He admits that he is the one who killed YUEN and NAM to avenge CHI's death. All are under his control and the plan is made up by him. It seems that the case has been solved but YUNG suspects that it is not the end as the mysterious man who attacked CHING is still unknown. Later YUNG finds that the one who attacked CHING is SUM, another tutor. However he is shot to die. As SUN has been arrested, there is another killer. YUNG suspects that the killer is CHING's boyfriend CHRIS as he knows much about the education centre. However who is CHRIS?