Though the South Pacific's Esa-ala Caves are some of the least-accessible on Earth, expert diver Frank McGuire (Richard Roxburgh) has explored them for months. On one such expedition, Frank is joined by his teenage son, Josh (Rhys Wakefield), and financier Carl Hurley (Ioan Gruffudd). When a flash flood cuts off their exit, they are caught in a life-or-death situation. With supplies dwindling, the divers must navigate a treacherous labyrinth to find a new escape route or die in the process.