On an ordinary morning, Tang Ning's son disappears in the stairwell; In the next unit, Lin Yutong, a young woman living alone, is assaulted in her sleep; Yan Wu, a gambling addict, is covered in blood and lies to hide a corpse. In this seemingly peaceful and inconspicuous apartment building, every "acquaintance" you pass by could be a monstrous demon hiding its fangs. When the human heart is more terrifying than ghosts, the door you enter and leave every day could be the entrance to hell......