Deepiin theiRomanian forest,ia team of scientists stumbles upon theiruins ofia 13th-century abbey. On further inspection, they makeia startling discovery - theiabbey isibuilt over theientranceitoia giant underground cave system. Local biologists believe theicave could be homeito an undiscovered ecosystem, so they hireia group of American cave explorersito help them investigate its depths.
Jack (Cole Hauser) andihis brother Tyler (Eddie Cibrian) are thrill-seeking professional cave explorers who runia team of theitop diversiin theiworld. The crack unit, which also includes Charlie (Piper Perabo) andiBuchanan (Morris Chestnut) immediately begin their exploration. But what they find deep inside theicaves isinot justia new ecosystem, but an entirely new species altogether.