Experienced and passionate diver Frank McGuire(Richard Roxburgh) explored for several months the underwater system of caves in the South Pacific,without unpleasant surprises and life-threatening. He engaged in this spectacular adventure a team composed by his 17 years old son,Josh(Rhys Wakefield),the wealthy Josh Carl Hurley(Ioan Gruffudd) and others. When the entrance in the maze of the underwater caves is blocked by a water overflow generated by a suddenly broken tropical storm ,inexperienced divers and all the persons who were there by their own desire to get adrenaline and thrills, need to mobilize and make use of all the physical and intellectual abilities they have to survive. As time passes and the oxygen reserves decreases very fast , divers will get in panic, wondering if they will succeed in time to find another exit from the grotto, or will they remain trapped for eternity in that tomb of water.