The film begins with a grieving Juno (Shauna Macdonald), who, along with her friends Cynthia (Natalie Mendoza), Alex (Alex Reid), and Sarah (MyAnna Buring), embark on a caving expedition in the Appalachian Mountains. The group, all experienced cavers, aims to explore a newly discovered cave system. However, their adventure takes a dark turn when they accidentally trigger a cave-in, trapping them deep beneath the earth's surface.