The Sealed Evening Study Classroom

At Nanchuan No. 7 High School, there's a late-study classroom that was sealed shut with chains long ago. Rumor has it that on the eve of every monthly exam, the sound of pages turning comes from inside at the same time, the answers to the next day's test appear on the blackboard, and one person who should have left the school building goes missing. Xu Chen, a transfer student in his second year of high school, only wants to make it to graduation in peace. But during his first turn on late-study classroom duty, he receives a seating chart from the sealed room. It lists every student's name, and someone has already drawn a black box after his.

Old school rules, missing graduates, names called over the late-night broadcast, and late-study sign-in sheets that always show one extra student... When the whole school starts to resemble a gigantic paranormal exam hall, Xu Chen realizes that the classroom was never what had been sealed away. It was everyone who wanted to leave alive.