There is a legend about the "disappeared study room 404" at the University of Nanhua - anyone who enters it on a full moon night will disappear. In order to verify the legend, {Xia Xiao}'s roommate broke into 404 on a full moon night and never heard from her again. In order to find his roommate, Xia Xiao conducted an in-depth investigation and accidentally discovered that a tragic fire occurred in 404 40 years ago: a student named Lin Mo died in the flames to save his classmates, and the rescued person turned out to be the current principal Gu Mingyuan. As the investigation progresses, Xia Xiao witnesses the reappearance of 404 on a full moon night, and Lin Mo's ghost appears, revealing Gu Mingyuan's crime of giving up rescuing people out of cowardice and instead using magic to seal the study room to cover up the truth. Xia Xiao went through hardships and dangers to collect evidence, and finally revealed the truth, lifted the seal, and all the missing students returned.
