Deep in the Romanian forest, a team of scientists stumbles upon the ruins of a 13th-century abbey. On further inspection, they discover that the abbey is built over the entrance to a giant underground cave system. Local biologists believe the cave could be home to an undiscovered eco-system, so they hire a group of American cave explorers to help them investigate. The crack unit arrives in Romania with all the latest equipment, including a new type of scuba tank that allows a diver to remain submerged for up to 24 hours. What they find deep inside the caves is not just a new eco-system but an entirely new species altogether.