The Descent, written and directed by Neil Marshall, is a British horror flick that had a wide theatrical release in 2005, including showings in America. The film is typical horror fare: A group of six adventurous women meet periodically to engage in risky and challenging activities, like rock climbing and white water rafting. The adventure depicted in this film--a spelunking expedition in a newly discovered cave in the Appalachian Mountain range--goes horribly wrong with for all the expected reasons.
A cave-in, that cuts off access to the outside world.
Hysteria among some of the group, which results in injury or death.
Large human-like bat creatures that live deep in the cave, and which hunt these women as they try to escape the cave.
Not your cup of tea? Mine either, really. Except for this one major twist:
One of the women in the group suffers an unexpected tragedy in the first few minutes of the film which changes her forever. An underlying presumption as the movie unfolds--it's almost a nagging suspicion more than a presumption, because there are no real clues to this--is that there are no real bat-like monsters at all, and the female lead character (played by Shauna Macdonald) is really behind the goings-on.
Marshall hints at this in several interviews.
Regardless of that plot twist, The Descent isn't a great movie. It's formula is pretty tired, the monsters are stereotypical and the acting is average at best.
The DVD issued in America contains an alternative ending that was originally trimmed to make the audience feel more hopeful about the outcome. The alternate ending, for me, is one of the weakest portions of the flick.