A half-dozen women friends meet in the Appalachians to explore a remote cave, hoping their outdoor adventure will rejuvenate one of them after a tragic accident a year earlier, but they’re attacked by blind subterranean beasties. Written and directed by Neil Marshall, this intermittently effective UK horror thriller carefully establishes the psychological relationships among the women, then squanders this calibrated and generally plausible setup with a series of crude, implausible, and scattershot horror effects. The two strains are supposed to merge but mix like oil and water as the narrative grows increasingly incoherent (the fact that so much of it transpires in darkness doesn’t help). Marshall changed the film’s ending after its successful British run, reportedly to dumb it down for the American audience. With Shauna Macdonald, Natalie Mendoza, Alex Reid, Saskia Mulder, MyAnna Buring, and Nora-Jane Noone.