"Four Americans on vacation don't just disappear," reasons medical student Jeff (Tucker) from his perch on a Mayan temple high above the Mexican jungle.

Oh but they do, Jeff. And in ways it's probably best not to think about.

Jeff and his girlfriend Amy (Malone) plus their holidaymaking buddies Stacy (Ramsey) and party animal Eric (Ashmore) have passed up on the beach to make a trip inland to see an off-the-beaten track stone temple.

Unfortunately, the locals have proven none too friendly. After blowing out the brains of a fellow day-tripper, they've forced the not-so-ready to party party high up into the ancient ruins and blocked any escape.

After their gory reception, there's obviously something nasty up there...but they don't know what. "This is so not OK," observes Stacy with a terrifyingly marked degree of grim prescience.

To reveal anymore would be to spoil what is one of the most efficient horror-thrillers in recent memory. One small pointer - it's what you'd expect from the writer of the brutally impressive A Simple Plan.

What follows is a genuinely chilling battle for survival against a, erm, creepy foe that initially appears innocuous yet displays a lethal intelligence and a disconcerting ability to mimic. Oh yes.

You'll need a strong stomach - once scene features a graphic DIY amputation and the wound cauterised with a smouldering frying pan for good measure. There's also one nubile filly slashing her body in a fruitless search for squirming parasites.

Yet at its dark heart lies a sound psychological brain-number enhanced by characters that - rare for a horror film - break out into three dimensions.

The ruins will leave you a wreck.

Tim Evans