On an annual extreme outdoor adventure, six women 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 rockfall blocks their exit and there's 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 - one that attacks without warning, again and again and again.