During a violent storm, Sarah Tyler (Isabella Calthorpe) returns to her troubled family home in the countryside for a much put-off visit. As the storm rages on, Sarah, along with her family and friends shore up for the night, cut off from the outside world. But something emerges from the driving rain and darkness... something that holds a dark secret so devastating that, in one night, it could wipe out everybody. Trapped, they must use their heads as well as their strength to survive. Can they survive the horror which is stalking them? Can they survive for 13 hours? Or is their enemy already amongst them and always has been?