After moving into an old, mysterious apartment building, new tenant Xiaoyan discovers all kinds of eerie things. There is no button for the fourth floor in the elevator, and horrible sobbing can be heard in the middle of the night, but the neighbors refuse to discuss it. As Xiaoyan searches for the truth, she meets a mysterious old man who is terrified whenever the fourth floor comes up. Summoning her courage, she takes the stairs to look for clues, only to find a tightly shut door between the third and fifth floors that she cannot push open. The sobbing comes from behind it. After asking around, Xiaoyan learns that a family was murdered on the fourth floor years ago. The floor was sealed off afterward, and people say it is cursed by vengeful spirits. When Xiaoyan decides to move out, a series of even more terrifying events befalls her, as though some evil force is haunting her. Her life is now in grave danger. In this fog-shrouded apartment building, can Xiaoyan uncover the secret of the fourth floor, escape the shadow of terror, and reclaim her life?
