At a time when the science-fiction label generally applies to big-budget space adventures with nothing on their minds, it seems fitting that Primer, the $7,000 debut feature of writer-director Shane Carruth, should bring the genre back to smart, idea-driven speculative fiction. An achievement at any cost, the film makes an asset out of its financial liabilities, because without the money for gleaming spectacle, it can only afford to tinker with the audience's imagination. Much like his brainy heroes, who run a scrappy tech-hardware business out of their garage, Carruth creates a homemade wonder out of available materials, stitched together with just enough credible pseudo-science to stoke an atmosphere of escalating paranoia and dread. And he does it all through little intangibles—subtle grace notes in the dialogue, a dense soundtrack, the suggestive use of screen space—that don't cost a dime.
An engineer who taught himself filmmaking, Carruth also stars as one of four young hardware developers who sweat over their obscure gizmos in a cluttered suburban garage. Unbeknownst to the other two, Carruth and David Sullivan are secretly developing an amazing invention that can disrupt the space-time continuum in ways both potentially lucrative and catastrophically dangerous. A time machine of sorts, their creation allows them to glimpse the future by manufacturing doubles of themselves, but they have to be careful not to make themselves conspicuous or alter events in an irreparable way. At first, they seize on obvious benefits like retroactively "predicting" the stock market, but when they start to lose the thread, matters quickly veer out of control.
Already swimming with technical jargon and logical conundrums, the last 30 minutes of Primer are nearly impossible to fully decipher on first viewing, and probably aren't much clearer several screenings later. This isn't a flaw. Carruth deliberately refuses to dot i's and cross t's, because at a certain point, the logistical ramifications of what his characters have done spin off into infinity, if not some sort of apocalypse. A brainteaser of the first order, Primer ranks among the best of recent thrillers such as Memento or The Matrix, which rupture the fabric of reality and radically destabilize the narrative in kind. While it's not always easy to gain a solid foothold, the resulting anxiety triggers the mind into concocting new solutions to explain what's happening, which is a far more frightening experience than knowing with any degree of certainty. As a riddle, Primer gains its seductive power by leaving the solution tantalizingly out of reach.