Directed by Alister Grierson. Starring Ioan Gruffudd, Richard Roxburgh, Alice Parkinson, Rhys Wakefield, Dan Wyllie 15A cert, gen release, 109 min

"JAMES CAMERON'S SANCTUM" trumpets the publicity for this half-arsed potholing adventure. You can see why the bearded box- office champ was an eager executive producer. Set within the deadly confines of The Biggest Cave In The World (the Esa'ala system in the South Pacific, apparently), Sanctumtrades on geek boy facts, technical specs and pure testosterone.

Based on the xtreme(!) caving explorations of Cameron's longtime collaborator, Andrew Wight, the film takes us on a journey through the unknown. Who could have imagined that the eerie, magnificent bowels of the earth contained such toxic levels of clunky exposition and rubbish plotting? Who knew anyone would want to remake The Abysswithout the feature creatures?

At the heart of a very sketchy “drama” we find young Bieber- alike Josh (Rhys Wakefield), a teenager who has been shanghaied by grizzled, estranged diver dad Frank (Richard Roxburgh) into a perilous expedition. The lad has far more time for Carl (why, Ioan Gruffudd, why?), the feckless, glamorous billionaire who financed the operation.

Then a massive tropical storm hits, leaving an entire posse of wannabe amphibians to find their way out of an unchartered underwater expanse. Now it’s Frank’s time to shine. He swims, he explores, he dispatches wounded comrades before the bends cause their blood to “fizz like a shaken can of beer”. Seriously folks, we’re supposed to cheer for the socially inept murderer.

Cameron's own specially developed digital 3D process, which he created for Avatar, is used here to terrific effect. Unhappily, the director's specially developed application for confoundedly awful dialogue is also here. The Aussie character insists on saying "dunny" or "tinny" in every sentence; the salty old diver Frank introduces himself as "a salty old diver"; the sheep, if there was one, would say "Baa".

Elsewhere, the same screenplay is not lacking in misogyny and product placement. It’s one thing to do boy’s own; it’s another when two biggest errors on the survival trek are attributed to the film’s token females. (“She made her own decisions,” tuts Frank.)

Plugs for National Geographiccome thick and fast – ironic, since most viewers will wonder why this isn't a National Geographicdocumentary. In this spirit, the caves are magnificent to behold. The 3D is involving. Such a pity somebody put this abyssal movie in the way.