The Descent

On her way back from whitewater rafting with her friends Juno (Natalie Mendoza) and Beth (Alex Reid), Sarah (Shauna Macdonald), along with her husband Paul (Oliver Milburn) and their daughter Jessica (Molly Kayll) get involved in a car accident when Paul is distracted. Paul and Jessica are killed, but Sarah survives.
One year later, Sarah and her friends Juno, Beth, Sam (MyAnna Buring), Rebecca (Saskia Mulder), and newcomer Holly (Nora-Jane Noone) are reunited at a cabin in the Appalachian Mountains of North Carolina. While spelunking, Juno apologises to Sarah for not being there for her after the accident, but Sarah is distant. As the group moves through a passage, it collapses behind them, trapping them. After a heated discussion, Juno admits she led the group into an unknown cave system instead of the fully explored cave system like they originally planned, and that rescue is impossible because of this. She then tells Sarah that she led them into the unknown cave in the hopes of restoring their relationship, but Sarah rebuffs her.
As the group presses forward, they discover climbing equipment from a previous spelunker, and a cave painting that suggests an exit exists. Holly, thinking she sees sunlight, runs ahead, but falls down a hole and breaks her leg. As the others help Holly, Sarah wanders off and observes a pale, humanoid creature (called "crawlers" in the credits) drinking at a pool before it scampers away. Later, the group comes across a den of animal bones, and are suddenly attacked by a crawler. Holly is injured and dragged away by the crawler to her death, Sarah is knocked out by a fall, and Juno accidentally stabs Beth through the neck with a pickaxe after mistaking her for the crawler.
Sarah awakens to find herself in a den of human and animal carcasses, and witnesses Holly's body being consumed by a crawler. Juno discovers markings pointing to a specific path through the caves. After regrouping with Sam and Rebecca, and realizing the crawlers' hunting methods, Juno tells them the markings she discovered may point to the way out, but she will not leave without Sarah. Meanwhile, Sarah encounters Beth, who tells Sarah that Juno wounded her and abandoned her, and also reveals that Juno had an affair with Paul before his death. In pain, Beth tells Sarah to give her a mercy killing, Sarah reluctantly does so by bashing her head in with a rock. She then encounters a family of crawlers, but manages to kill them all, being covered in blood in the process. Afterwards, she has a psychotic breakdown. Elsewhere, Juno, Sam, and Rebecca are pursued by a large group of crawlers. Sam and Rebecca are killed, but Juno escapes.
Juno encounters Sarah and lies to her about seeing Beth die. After defeating a group of crawlers, Sarah confronts Juno, revealing that she knows that she wounded Beth and left her for dead, and also about the affair. She then strikes Juno in the leg with a pickaxe and leaves her to die to a group of approaching crawlers. Sarah falls down a hole and is knocked unconscious. She awakens, manages to escape the cave, runs to her vehicle, and speeds off. Upon seeing Juno sitting next to her, Sarah screams and reawakens to find herself still in the cavern, revealing that the events since her previous awakening were a dream. She hallucinates about a smiling Jessica close by her, just as the calls of the crawlers grow louder.
Alternate versions[edit]
For the US theatrical release, the film ends with the appearance of Juno in the car, and the scene where Sarah hallucinates her daughter in the torchlight was removed entirely. The Unrated DVD released in the US includes the original ending. This ending leads to the events of the next film.[3]

Question: What is the group attacked by?
Answer: Crawler