Jack (Hauser) and his brother Tyler (Eddie Cibrian) are thrill-seeking professional cave explorers who run a team of the top divers in the world. They arrive in Romania with all the latest equipment, including a new type of scuba tank allowing a diver to remain submerged for up to 24 hours. The crack unit, which also includes Charlie (Perabo) and Buchanan (Chestnut) immediately begins their exploration. But what they find deep inside the caves is not just a anew eco-system, but an entirely new species altogether…