In a remote mountain range, six female friends 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 rockfall. 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. But left with no 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. But there is something else lurking under the earth, a race of monstrous creatures hidden from the light, devolved to perfectly live in the dark… As the women realize they have become prey, they are forced to unleash their most primal instincts to face the creatures. But, as old wounds break open and loyalties disintegrate, the women realize the horrible truth—that they have most to fear from one another.