Blood-thirsty creatures await a pack of divers who become trapped in an underwater cave network.

Decades after a rock church in communist Romania's Carpathians caved when an expedition caused a landslide and buried everyone, Dr. Nicolai's scientific team exploring the associated Templar Knights monster fighting-legend discovers a deep, flooded cave system and hires the brothers Jack and Tyler's brilliant divers team to explore it. Another explosion traps them, after finding a mysterious parasite turning all species carnivore, and later an independently evolved predator species. Jack may be infected and turning, but Tyler sticks with him, so the group splits, hunted by the monsters, which also fly.—KGF Vissers

On the remains of an abandoned convent in the Romanian Carpathian Mountains, a team of archaeologists discover the entrance to a massive cave system and intrepidly, they decide to explore it to the end. With the intention to further investigate the existence of a rare virgin and unspoilt ecosystem, under the leadership of Dr Nicolai and his trusted associate Dr Kathryn Jennings, a group of seasoned cave divers led by Jack McAllister is assembled. Equipped with the latest in modern technology, the researchers will ambitiously begin their expedition deep inside the heart of the mountain, in what seems to be a vast interconnected network of undiscovered caverns. However, as they gradually progress deeper into the earth, four kilometres underground, a completely unknown and extremely hostile life form awaits them exposing the mountain's deadly secret which will sooner or later, engage the team in a battle for survival between species.—Nick Riganas

A group of cave-divers and scientists explore a newly found cave system in Romania. However, rockfall blocks the exit and after delving further into the cave, the group discover a pack of deadly creatures are waiting for them. With their leader Jack having very strange side-effects and with their numbers dropping, the group must delve even further into the cave, battle the creatures and hope for an exit.—MovieFan998

Thirty years ago, in the Carpathians Mountains of Romania, a group of explorers blows an entrance to a cave hidden under a church, but the explosion causes a landslide and they become trapped inside. In the present days, the expedition leaded by Dr. Nicolai and his assistant, Dr. Kathryn are exploring the place and they find the access through an underwater river, requesting the experienced cave divers team leaded by Jack. Dr. Nicolai discovers that, in accordance with the local legend, the church was built to seal the cave as a display of God's protective power, and that Templar Knights entered the cave to fight winged demons. When the group reaches a cave though a tunnel one mile below and three miles in, a creature attacks one of the members and his breathing apparatus explodes, collapsing the tunnel and trapping the group in the cave. Soon they realize that they are the rescue team and they have to find an exit to survive from the attack of the monsters.—Claudio Carvalho, Rio de Janeiro, Brazil