Jack (Cole Hauser) and Taylor (Eddie Cibrian) are two cave experts who love exploration. At the invitation of biological experts Nicola (Marcel Iures) and Dr. Janice (Lena Headey), they brought an experienced team to the Carpathian Mountains in Romania to investigate the huge caves and ancient churches that were accidentally discovered here. Expedition member Briggs (Rick Ravanello) was the first to go into the water for investigation, but he lost contact with his teammates shortly after the communication. For safety reasons, Jack and Taylor decided to set out to search together. Along the way, they saw all kinds of strange creatures that they had never seen before. It turned out that in this closed cave, there was a completely independent paleontological system. However, these discoveries did not bring them too many surprises. The explorers were trapped in the cave, and the threat from unknown creatures was gradually approaching them...