Xiao Ze is a criminal police captain in Yan Hai City who receives a call about a suspicious death in Xingning Community. A neighbor reported smelling blood and seeing dried blood under the door of a young woman's apartment. When Xiao Ze and his team break down the door, they find a woman's corpse in the bathroom. The deceased, Zhou Yun, is a twenty-year-old university student with her right carotid artery severed. The scene appears cleaned meticulously, with disinfectant smell mixing with blood. Xiao Ze suspects this may be connected to a series of serial murders in another city where victims were also young women and wax blocks with taunting messages were left on their bodies.
The case takes a turn when Gu Yuan arrives as the new forensic doctor. Gu Yuan is a young man with an ethereal appearance, pale skin, and cold demeanor. He has studied in the United States and returns to work in his hometown. Gu Yuan examines the body and determines the cause of death is hemorrhagic shock from the neck wound. He notes the victim was left-handed based on a callus on her left middle finger. The murder weapon is identified as a razor blade found near the body. Gu Yuan also discovers needle marks on the victim's arm and finds she was pregnant with a three-month-old fetus. Inside the victim's body, he finds a wax block containing a note that reads "The vile shall die."
Gu Yuan investigates an online forum where a blogger posts about suicide methods. He notices the murder methods in previous serial cases match the posts' order. This leads him to suspect the forum is connected to the crimes. Meanwhile, Mo Lin, a criminal psychology consultant, arrives to assist. Mo Lin is charismatic and observant, quickly analyzing the case. He determines this is not a serial murder but a crime of passion, with the killer imitating the serial murderer's methods to frame someone else.
Through interrogation of the victim's boyfriend Ni Bin and friend Li Zheng, Mo Lin uncovers that Zhou Yun was involved with multiple men. Li Zheng, a nurse from Yunshan County, confesses to the murder. He had loved Zhou Yun since childhood but felt inferior due to his poverty. Zhou Yun used him for money while seeing other men. Upon discovering she was pregnant with another man's child, Li Zheng killed her in a fit of rage. He injected alcohol into her vein to intoxicate her, then slit her throat. Afterward, he placed a wax block in her body to mimic the serial killer's signature.
The case reveals Gu Yuan's emotional detachment and social anxiety. He struggles with close interactions and prefers solitude. Mo Lin takes an interest in Gu Yuan, inviting him to examine the serial murder case files at his home. They discuss the three previous victims: a flight attendant, a kindergarten teacher, and a nurse. The killer left wax blocks with words: "First Night," "Game," and "Lie." Mo Lin speculates the killer targets these professions due to resentment.
As the investigation continues, a new body is found near the airport—a flight attendant killed in the same manner as the previous serial murder cases. The killer has resumed his original pattern, suggesting Li Zheng's imitation may have provoked him. Gu Yuan and Mo Lin work together to analyze the new crime scene, discovering that the killer destroyed surveillance cameras before the murder. The story sets up a race against time to catch the serial killer before he strikes again, while Gu Yuan and Mo Lin's professional relationship begins to develop despite Gu Yuan's discomfort with social interaction.
