Driven mad and barely alive with fear, Sarah Carter emerges alone from the Appalachian cave system, where she and her friends encountered nightmarish supernatural phenomena. She is unable to give the authorities a plausible explanation of what happened or why she is covered in her friends’ blood. She also reluctantly agrees to return there to help search for the other five girls. The rescue expedition ventures deeper into the uncharted caves, and nightmarish visions of the recent past begin to haunt Sarah once again—she is the only one who fully realizes the sheer horror and futility of the mission.