Dayin Dynasty, Yongping period. Under the prosperous imperial capital, there is a shocking "Forbidden Book of Xu Shi" hidden. What is recorded in the book is not gold and silver, nor is it the secrets of the court, but is an incredible "rule" written in blood and ink. At three o'clock in the morning, the dusk drum beats, the city gate is locked, and the city is closed. This thin book will quietly appear on the pillow or desk of certain specific people, or even be directly imprinted on the mind. The rules are absurd and weird: "At three o'clock in the morning, you are not allowed to hold a lamp to look at shadows." Shen Yan, a down-and-out scholar who possesses "night eyes" and can see things invisible to ordinary people, is accidentally involved. In order to protect himself and to find out the truth behind the mysterious disappearance of his best friend, he was forced to go with the mysterious mute Liu Qixian and embark on a thorny road to survive in the taboos of the time of Xu. Not only do they have to crack the endless life-threatening rules, but they also have to fight against the strange existence lurking in the darkness, and step by step uncover the shocking secrets behind the "Forbidden Book of Xu Shi" that can overthrow the dynasty and subvert Yin and Yang. When the ancient curse intersects with the shadow of imperial power, and the boundaries between life and death become blurred in the bells of Xu Shi, can they find a glimmer of hope amidst all the taboos?
