At Herrington High School in Ohio, it seemed that overnight, the school's teachers and some of the top students became very strange. They used to have a kind attitude, but now they are cold and gloomy, and this situation seems to be getting worse.
Troubled students Casey (Elijah Wood) and Delilah (Jordana Brewster) accidentally hide in the closet, and in doing so, witness the brutal murder of nurse Rosa (Salma Hayek). But it wasn't long before Rosa appeared in front of everyone intact, but her expression was as grim as that of the other teachers. Casey and the others gradually realize that this chain of events is related to some mysterious creature they have discovered, and now it seems that this creature is spreading at an unimaginably terrifying rate. Danger looms......