Three cases of rape-and-murder have occurred recently. The three victim were strangled to death by the killer and neither finger- prints nor sperms can be found. The police force set up a special team to handle the case. MAN is transferred to YUNG's team to give him a helping hand. YI also returns after his vacation. YUNG finds that the three victims uses the perfume “Envy”. It has special scent and is not popular. Few customers use it. Incidentally YUNG discovers that CHIT's uncle WAI had taken photographs of the three victims in his studio before the tragedies occurred. WAI is suspected. They keep an eye on WAI and finds that he courts DAISY. They go to a hotel and after thirty minutes. the girl screams for help.

It is find that WAI and DAISY quarrel as they cannot compromise with the price involved in the filthy transaction. YUNG also finds that WAI's behavior is different from that of the murderer. However a witness recognizes that WAI was with the third victim before being killed. WAI admits that that night he escorted her home but after that he returned to his studio. As there is no one proving' WAI's statement, he cannot prove that he is innocent. WAI’s counsel KIT and four waiters claim that WEI was in the coffee shop of a hotel and he wore an orange jacket. As the jacket has been sent to a laundry, KIT's statement is not accepted. In fact WRI tries to hide the truth as his filthy relationship with the owner of the hotel may be disclosed. The fourth case occurs and ADA is the victim. Luckily ADA regains her consciousness.

ADA reports that she was attacked by the sex maniac from behind and she fainted. YUNG gets an idea and they narrow down their scope of investigation to doctors and YUNG- finds that doctors have more chances to be close to their patients. After checking it is discovered that all the four victims were clients of St. Peter's Clinic. SUT, MING and CHAI are suspected as they' are doctors there. MAN is instructed to go to the clinic to bait the real murderer with “Envy”. She takes refuge in a unit being protected by the police. The killer arrives but is frightened by the alarm of the life which is out of order. YUNG sees the car of the villain and they focus on SUT and CHAI as they have the car of the similar style. It is found that SUT had bought a bottle of “Envy” near MAN’s unit and then he disappeared. It is rather certain that SUT is the sex maniac as the four victims’ records are found in his house.… ...

However medical checking shows that SUT had been poisoned to a comatose state before being killed in the traffic accident. Moreover there is no finger-print on the steering wheel. It is certain that it is a set up murder. YUNG and YI rush to save MAN but it is too late. MAN has been kidnapped by CHAI. Seeing that he has been surrounded, CHAI releases MAN and goes to the roof, trying to kill himself. CHAI committed the cases as he was shocked by his wife who had betrayed him. The situation worsened as he found that his son was not his flesh and blood. His anger explodes when he met the victims with “Envy”. His wife had a gift of “Envy” from her secret lover. He went insane and calmed himself by killing the victims. When he knew that he was suspected, he used tricks to frame SUT but in vain. He has to face trial by the law.