A man (Joel Edgerton) lives together with his wife (Carmen Ejogo) and son (Kelvin Harrison Jr.). The trailer shows that Joel takes in a young family looking for shelter. The only thing they need to do is follow a couple of house rules: During the day, you go out in groups and during the night, you stay inside. A red door keeps the outside from getting in and it must be closed at all times. Obviously, the door is left open and terrible events unfold.