Chang''an is drowned in a sudden dense fog, and people flee in panic. In order to protect the weak prince, the official Xiao Cheng is trapped with the civilians, waiting for the fog to dissipate. However, the fog does not disperse as expected, and the people who walk into the fog never return. The frightening monsters in the fog gradually reveal their ferocious features. Xiao Cheng fights to his death to protect Chang''an.