Sarah (Shauna Macdonald), emerges dazed, bloodied and half–wild with fear from a cave system in the Appalachian mountains. The local Sheriff is skeptical of her account of events and, convinced that her psychosis hides far darker secrets, forces her back into the caves to search for her five missing friends, unaware that a new breed of crawlers awaits them. More evolved and viciously feral than Sarah has ever faced.