The film is about a caving expedition six women friends in the American Appalachians. One of the girls, Sarah, still processed the trauma of a car accident in the previous year, in which her husband and her daughter died, but she survived. Since then, she has a recurring dream of her daughter with a birthday cake. As leader of the group organizing the trip Juno, which also Beth, the enthusiastic extreme athlete Holly and the two sisters, Rebecca and Sam van Ney.
After a night in a mountain hut Juno leads the five friends to the entrance of a cave system, which they believe is that the tourist Boreham Caverns. They abseil off and soon thereafter separately through a narrow tunnel. Sarah remains as a last stuck in the tube and gets a claustrophobic panic attack. Beth crawls back to Sarah and tried to calm them, but the response is unstable and crashes immediately after Sarah has liberated itself and the two fled the aisle have left, collapses.
Since they closed the back, Juno admitted in a subsequent dispute, that they are not in the Boreham Caverns, but in an unnamed and unexplored cave system, which they and their friends wanted to jointly explore.
When crossing a deep gaping gap Rebecca discovered in the cave ceiling an ancient Kent of a past expedition, but the still unnamed cave could never have left. As Holly then phosphorus reflections in rock for daylight, and the unwary entlanghastet the tunnel, crashing them buried in a gap and broke the leg. The girlfriends abseil down to her leg and appeared before the pain screaming Holly. Sarah away from the scene of an accident in a side cave, as she believes a child's laughter to be heard. They discovered a rusty helmet, and shortly thereafter immersed in a further distance pale in the light cone shape their torch, which is rapidly removed. Your friends do not believe Sarah's stories and run with a reference to a deceptive calm.
When they cave drawings, they recognize that there is a second source, and must decide, in this system of endless corridors, rock cracks and caves to search. It turns out that they are not alone. The cave system live strange, as ugly as blind crawlers, people not so dissimilar, but completely to life in the darkness. Their only goal: Fresh meat! For the women Embittered begins a fight for survival, in which not only the crawler their enemies, but also mutual distrust, the pervasive darkness and paranoia.
Already at the first battle against the onrushing crawler is Holly fatally injured. The others fled, but remains behind Juno and kills a crawler, which will bring Holly corpse. In the excitement of the crashes they herbeieilenden Beth from behind an ice ax accidentally in the neck and lets it after Beth chain from her neck has wrenched back. This keeps secret to the others. But Sarah finds the dying Beth, which warns them against Juno. Sarah It passes the chain, which Juno husband of Sarah's got.
After some further struggles remain ultimately only Juno and Sarah left. The two heard a group heraneilender crawlers. Sarah shows the chain of Juno Beth, it proposes an ice ax in the Wade and lets them in the back crawlers. It even runs away, but a little later crashing into a gap. She has the vision that she finds the outcome there, escapes from the cave and still in panic flees with her car. But then they realized that this was only a dream. In the final sequence, she sits in total resignation on the cave floor and waits for her fate.