Build a movie plot around this: With the equipment they have, how long will the divers be able to stay under water? Up to 24 hours.

This article's plot summary may be too long or excessively detailed. Please help improve it by removing unnecessary details and making it more concise. (June 2016) (Learn how and when to remove this template message)The film begins deep in the Carpathian Mountains of Romania during the Cold War, where a group of Russian and British explorers are searching for a long-lost 13th-century Eastern Orthodox abbey. As they venture inside and below the church, they make a startling discovery: the abbey is built over the entrance to a vast subterranean cave system. When they try to blast their way in, they cause a landslide that buries the abbey and the men are trapped in the cave below it. Once they recover, they continue on into the cave without a choice in hopes of finding a way out, but as they do, they hear strange sounds coming from the darkness.Thirty years later, a team of archeologists are excavating the ruins of the same abbey, where they unearth images of a medieval battle between the Knights Templar and winged demons, and discover the cave system with its massive underground river. The team is led by Dr. Nicolai (Marcel IureÅ) and his associate Katheryn Jannings (Lena Headey), along with her cameraman Alex Kim (Daniel Dae Kim). Local biologists believe the cave could contain an undiscovered ecosystem, so they hire a group of American spelunkers led by Jack McAllister (Cole Hauser) and his brother Tyler (Eddie Cibrian) to help them investigate its unknown depths. Jack and Tyler are thrill-seeking professional cave explorers who run a world-famous team of divers. They arrive in Romania with the latest equipment, including a modified rebreather system allowing a diver to remain submerged for up to 24 hours. The diving team includes rock-climbing professional Charlie (Piper Perabo), first scout Briggs (Rick Ravanello), sonar expert Strode (Kieran Darcy-Smith) and survival expert Top Buchanan (Morris Chestnut).As they begin the expedition, Briggs is sent to scout and when contact is lost they decide to press...