Tao Zhenyan, a trainee forensic doctor in the Republic of China, met Gu Nanchuan, a private detective, because of a murder case. Their fates were connected due to the emergence of the stamp demon serial killer, and they began to join forces to solve strange cases. Relying on Tao Zhenyan's excellent forensic knowledge and Gu Nanchuan's rigorous reasoning, one case after another cleared up the fog to reveal the truth. Thousands of clues between the cases point to the stamp devil's reappearance in the world. Back then, Tao Zhenyan's brother was sentenced to be a stamp demon and lost his life. For this, her family was infamous for the murderer's blood. Gu Nanchuan's parents were both killed by the demon stamp, and the two of them were at odds with the stamp demon. Together, a confrontation between good and evil begins.