On an annual extreme outdoor adventure, six women friends meet in a remote part of the Appalachians to explore a cave hidden deep in the woods. Far below the surface of the earth, disaster strikes when a rock fall blocks their exit and there is no way out. The women push on, praying for another exit, but there is something else lurking under the earth. The friends are now prey, forced to unleash their most primal instincts in an all-out war against an unspeakable horror that attacks without warning.