Though it is one of the least-accessible cave systems on Earth, skilled diver Frank McGuire (Richard Roxburgh) has explored the South Pacific's Esa-ala Caves for months with his team (Ioan Gruffudd, Rhys Wakefield) . When a flash flood cuts off their exit, suddenly they are caught in a life-or-death situation. With supplies dwindling, the divers must navigate a treacherous underwater labyrinth to find a new escape route or else die in the process.