Recently separated from her husband (Skeet Ulrich), Jess (Michelle Monaghan), a nurse and mother, moves with her daughter Tyler and young son Owen back into her old farmhouse. Shortly after settling in, Owen’s dog escapes into the woods and returns days later, blood-soaked and rabid. When he attacks and bites Owen, the resulting infection from the bite grows more alarming by the day as Owen’s behavior becomes frightening and deadly. As he spirals deeper into the depths of the illness, Jess discovers a disturbing cure, which makes her question how far she is willing to go to keep her child alive.