Frank (Richard Roxburgh) is considered to be the foremost underwater cave explorer. His teenaged son Josh doesn't like dad very much since he's so consumed by his work--and has never paid much attention to him. In fact, Josh really doesn't like assisting his father, especially on this new exploration of a cave system in New Guinea.
Everything is on schedule until there's a surprise flash flood above ground, which of course flood them out underneath. They can't get out the way they came in so they have to find the exit of this unexplored cave system into the sea. Among them is the father's assistant and Publicist Carl (Ioan Gruffudd of FANTASTIC FOUR), who has brought his headstrong girlfriend along. One by one they meet horrible demises, especially in the "meat grinder" scene in which they have to cross a fiercely bubbling cauldron. As this happens, seemingly easy-going Carl transforms into the bad guy, ultimately only concerned with is own survival. In the end only one of the trapped explorers survives.
Although there are no insectoid monsters, giant worms or even mutated humans, like in THE DESCENT, this movie is as harrowing and entertaining. It's visually stunning. Highly recommended.