Tao Zhenyan (played by Dong Yan), a trainee forensic doctor in the Republic of China, met private detective Gu Nanchuan (played by Gao Mingchen) because of a murder case. Their fates were linked by the appearance of the stamp demon serial killer, so they started to join forces to solve strange cases. With Tao Zhenyan's excellent forensic knowledge and Gu Nanchuan's rigorous reasoning, the truth of each case was revealed. The countless clues between the cases pointed to the stamp demon, which reappeared in the arena. At that time, Tao Zhenyan's brother was sentenced to death for the stamp demon, and her family was saddled with the notoriety of the blood of the murderer. Gu Nanchuan's parents were both killed by the demon stamps. The two were irreconcilable with the stamp demon, and a confrontation between good and evil began...