We begin the story with Du Ming meeting a beautiful lady named Zhang Qian. They begin their relationship by having long talks but they never fully become lovers.

Fast forward Du Ming is now a doctor at a hospital. He receives a letter about Zhang Qian committing suicide. Zhang Qian has difficulty accepting what happened and sometimes he sweats profusely.

During this time Du Ming learns one of his nurses was raped from one of her co-workers. She pleads with him to deal with the rapist. Du Ming decides to help her.

Du Ming decides to visit where Zhang Qian lived and he met her roommate. Her roommate was a slut and she revealed to Du Ming that Zhang Qian killed her self by hanging her self while sitting down. We learn why she did this in a flashback. In the flashback Du Ming and Zhang Qian had a conversation about death. That hanging oneself by sitting down achieves immortality. Which is why she hanged herself in such an odd way.

After this we witness Du Ming (in a flashback?) walking into a sewage facility. We see him looking at fat decomposing body which hints he probably murdered and knows that man.

Du Ming has also been helping the nurse by killing and incinerating her rapist so that no evidence is left behind. He still thinks greatly about Zhang Qian.

In the final chapters Du Ming is reading the journal and letter of Zhang Qian. We learn that Zhang Qian was an ideal beautiful student at her college. She met a wonderful guy and fell in love. However, the guy merely wanted to sleep with her as a bet and ended up raping her. She tells the school about what he has down and gets him expelled. However her family loses face and abandons her. The rapist gets revenge by having his friends gang rape her, leaving her forever scarred. Even after she is bullied intensively at school.

At the end it finally reveals that she slept with Du Ming's teacher in order to have him give Du Ming his Certificate of Graduation. Du Ming after recieving his certificate confesses to Zhang Qian. Zhang Qian however, rejects him for she was too impure for Du Ming. Du Ming runs away but somehow he realizes something has happened. (Somehow) Du Ming finds out that Zhang Qian slept with the teacher just so he could get his certificate. Du Ming in a fit of rage tortures and murders the teacher that had his way with Zhang Qian.

Fast forward a bit Zhang Qian somehow comes across the body of the teacher Du Ming murdered for her sake. She laments at how Du Ming who she idolized as being pure and kills herself. In the ending chapter the nurse ask Du Ming if he will ever get caught for murdering her rapist. He simply says we will be fine.

Zhang Qian was raped and abused
Zhang Qian helped Du Ming get his certificate to graduate and become a doctor by sleeping with his teacher
Du Ming confesses to Zhang Qian but she rejects because she fears she is too impure and he is too pure and too good to be with her. She doesn't tell him that she slept with the teacher.
Du Ming however suspects this and murders the teacher
Zhang Qian finds the body and commits suicide because the person she loved is now impure leaving her broken because Du Ming was always pure, but because what he has done breaks her spirit.

While this is all happening Du Ming is asked by a nurse to murder her rapist.

I thought he was gonna go crazy and kill that nurse who likes him...but instead he asks the nurse to 'be mine' ? what about zhang? I thought he was obsessed with her...

I also thought that Du Ming might kill that nurse; the ending was really unsettling. I agree with the explanations above, though it looks like he has still harbor some love to Zhang. I also think that he would be incapable of loving anyone at this point. Makes me wonder who was the most "pure" character in this story.

Basically the one who had raped the nurse was Du himself because he wanted to create a sinner who could be by himself.And secondly the nurse killed the doctor not Du Ming.I was confused at first also because the story shows us Du killing someone.But that was professor Wang who had made a deal to have sex with Zhang Quian so as to give Du his college decree.

His fatigue, which is shown through his habit of oversleeping appointments, can be attributed to his nightly crimes, mainly murders and the disposal of the bodies at night. He has adopted a certain routine when it comes the act of killing (another trait to characterise him as a serial killer) which is illustrated by the case of Zhang Qian's roommate: First, he invites his victim to the anatomy lab. There he commits the murder and afterwards, he drains all the blood from the body with a vacuum tube in order to make the transport easier. Since it's a medical facility used to prepare anatomical specimen, nobody would suspect anything if there were traces of blood or bowel. Then he moves and drowns the bloodless corpse in the sewage to get rid of it.