Symbol of Sin

Psychologist Qin Lan was recruited by the police to assist in investigating a series of murders with a strong sense of ritual - the victims were all injected with sedatives and then strangled to death. The bodies were carefully placed in confessional poses and had mysterious symbols engraved on their bodies. When she discovered that the first deceased was a high school classmate she had lost contact with for many years, and that the other person's phone contained his contact information, Qin Lan realized that the case was secretly related to her. As the investigation deepens, more victims emerge, and without exception they are all related to the "confessor psychological experiment" led by Qin Lan's father twenty years ago. Experiment records show that 12 subjects were forced to face the deepest sins in their hearts, and now, they are dying one after another in a "repentant" posture. What is even more disturbing is that there are clues leading to Qin Lan at each murder scene, as if the murderer is leading her to uncover a deliberately buried truth. When Qin Lan found a photo of her missing father in the hands of the latest victim and saw the bloody words "The fourth is the betrayer" on the wooden sign, she had to suspect that the father she had been looking for for twenty years might be the instigator of all this...