Protagonist Lin Shinian is able to interpret and intervene in rules. To search for his missing younger sister, Lin Xiaolu, he steps into the Seventh Sanatorium, which is eerie at every turn. Talking walls, fellow patients wearing paper masks, the sound of suonas at the midnight carnival, together with the gentle yet dangerous Dr. Lu, weave a net of memory-devouring rules. Teaming up with fellow patients Chen Tie, Su Xiaomi, and Gao Ye, he repeatedly cracks the rules of life and death, ultimately making the sanatorium cease operations and rescuing his sister. However, a Ninth Apartment check-in code of conduct is quietly mailed over—this time, he chooses to take the initiative and challenge the new rule-based horrors.