Sarah Tyler returns to her troubled family home in the isolated countryside, for a much put-off visit. When a storm errupts, 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 that holds a devastating secret that could wipe out the entire family. Trapped, they must use their heads as well as their physical strength to survive not only the thing that is hunting them down one by one - but their own entrapment as the besieged group turns in on itself. Can they survive the horror which is stalking them for 13 hours, or is their enemy already amongst them, and has it always been?