Chengnan Middle School's "zero point for evening self-study" is a taboo that previous students dare not touch – at 22:00 every night, the teaching building will plunge into absolute darkness for 3 minutes on time, and during these 3 minutes, there will always be "things" taking the opportunity to mingle with the crowd. Transfer student Lin Shen (male protagonist) discovered something strange in the darkness as soon as he arrived at school: a shadowy figure wearing an old school uniform repeatedly picked up non-existent pieces of chalk in the corridor, while classmate Su Wan (female protagonist) was holding a camera and calmly filming this scene.
The "Abnormal Investigation Club" where Su Wan belongs is a small group marginalized by the school: the president is Zhang Ye, an academic who is obsessed with occultism, and its members include Li Mengmeng, an introverted girl who can hear "whispers", and Zhao Peng, a tech geek who firmly believes that everything can be explained scientifically. They have long discovered that the strange events in the school go far beyond the "zero point" - the on-duty student disappearing into the toilet cubicle, the swing that automatically rotates in the corner of the playground, the books that change positions on their own in the library... These events seem to point to a fire twenty years ago, and the students who disappeared in the fire are said to still be looking for "unfinished homework" in the teaching building.
After Lin Shen was forced to join the Investigation Club, he discovered that he could clearly see the faces of "ghosts" in the dark - those faces were exactly the same as those in the school history photos. As they investigate further, more and more people begin to "disappear" after 22:00, and the last words left by the missing people are always "Don't look back, the blackboard is watching you"...
