Wen Zhi, a sophomore broadcasting student, works part-time as a night shift attendant in the girls' dormitory. She finds a bizarre duty rulebook left behind by her ex: after eleven-thirty, do not open the door if there are more than seven knocks, and do not answer when someone calls your name in the hallway. Strange events occur one after another, but others only hear static in the recordings of abnormal sounds she made. The dormitory head suspects she is mentally unstable and wants to cancel her night shift. Relying on her sharp hearing as a broadcasting student, Wen Zhi sets up a trap to ferret out the hidden stranger, and with an anonymous access card, uncovers the secret of the hidden mezzanine on the sixth floor.