In a remote mountain range, six girlfriends meet for their yearly adventure, a caving trip into the arteries of the earth. The group makes their way through the remote cave system, enjoying the hazardous but beautiful surroundings. Then, deep inside the cave, disaster strikes when their route back to the surface is blocked by a rock fall. When they learn that Juno, always pushing herself that little bit further, has brought them to an unexplored cave, and that no one is coming to rescue them, the group starts to splinter. Left with no other option, they push on through the cave, praying for another exit. The women battle through this harsh underground world, pitting their strength and determination against each new challenge. Unbeknownst to them, there is something else lurking under the earth, a race of monstrous creatures hidden from the light, evolved to live perfectly in the dark. As the friends realize they have become prey, they are forced to unleash their most primal instincts to face the creatures. As old wounds break open and loyalties disintegrate, the women realize the horrible truth-they have most to fear from one another."