NOW THAT ADVANCES in CGI have afforded even the most cost-conscious filmmakers the opportunity to expand their horizons and hide the seams, there's something heroic about those who choose not only to work within their limitations, but to handicap themselves even further. The ferociously high-concept Buried feels like something Hitchcock would have pulled off on a dare during a long weekend, which is nearly the highest praise I can give. Claustrophobes and those prone to ADD probably need not apply, but within its self-determinedly narrow boundaries, it's just about unimpeachable.

Chris Sparling's script has a sketched-on-a-cocktail-napkin purity: A man (Ryan Reynolds) wakes up in a wooden casket underground, with only a half-charged Iraqi-language cell phone and a flickering Zippo for companions. The camera never steps outside for air. Sparling and director Rodrigo Cortés score some pungent, ironic points concerning current political and economic policies, but never at the expense of raising the stakes and finding ways to make a bad situation even worse. For 90 solid minutes, they keep turning the screws.

Thematically and technically ingenious as Cortés's film is, though, it likely wouldn't register as more than a tooth-grinding novelty without the performance of Reynolds, an actor who generally gives the impression of amiably being above his material. (Which, admittedly, isn't much of a knock, given most of his films.) Here, though, he commits totally to playing far against type, as a not-exceptionally-bright everyman stuck in a situation way beyond his ken. His efforts transform what could have been a chilly technical exercise into something darkly comic, unexpectedly moving, and, above all, hot-plate skittery. You will squirm.