"Who's Knocking"
The lives of Lu Lin and Su Qing were interrupted by repeated knocks on the door late at night. As a criminal police officer, Lu Lin has just taken over an unsolved case that has been hanging around for ten years. Su Qing, who lives alone, becomes the target of a mysterious knocker - there is no one inside the door, and only a rusty old key is left outside.
The old key involves the belongings of the victim of the unsolved case, and Lu Lin discovers that Su Qing's life experience is closely connected to the case. Every knock on the door is accompanied by strange clues: disappearing footprints, bloody notes, midnight whispers. The two were forced to join forces to investigate, but found that the person knocking on the door seemed not only to come for the truth, but also to force them to face the crimes that were covered up ten years ago.
When the knock on the door rang again and the shadow behind the door gradually became clear, they were shocked to realize that the most terrifying thing was not the unknown fear, but the secrets hidden by the people around them.
