Dominic Cooper gives a stunning double performance and Lee Tamahori reminds us of his skill as an action director in “The Devil’s Double,” but the film itself is a one-note affair that’s impressively made but ultimately little more than a stunt—and one that’s hard to swallow as well.

That’s because it’s based on the memoir of Latif Yahia, an Iraqi soldier who was forced to serve as a stand-in for Uday Hussein, Saddam’s reckless, lustful older son. The problem is that the script simply follows Yahia’s contention that he was a highly principled fellow compelled by threats to his family to submit to the volatile Uday’s demands, and that he always tried to do the right thing in torturously difficult circumstances. That certainly makes for a clean scenario, but one can’t help but suspect that things were actually a bit more morally ambiguous than that.

The yarn begins with Yahia brutalized by Uday’s henchmen until he agrees to become the madman’s double and then being subjected to surgery to duplicate the other man’s appearance as closely as possible and trained to imitate his wild-eyed manner. After that prologue is finished, the picture takes off into Uday’s life of complete abandon as he hosts lavish parties, abuses anybody who crosses him in the slightest, and beds whatever females catch his ever-roving eye, including a bride he whisks away from her groom on their wedding day (who kills herself after he rapes her), and schoolgirls he abducts off the street (their bodies are dumped in the desert after he’s done with them). Throughout Uday is portrayed as the very image of the unrestrained id, while Latif, looking on with undisguised contempt, becomes the conscience the dictator’s son totally lacks (and the viewer’s convenient surrogate).

Throughout these episodes, Cooper and Tamahori really go for broke. The actor wallows in Uday’s ostentatious malevolence, making much of his toothy grin as he seduces and his fury when he slaps, pistol whips or simply shoots those who displease him, and though he can’t show similar glee while embodying the dour, serious Latif, he does an excellent job keeping to two distinct even when the double is doing his impersonations. It’s a virtuoso turn, and Cooper nails it. As for Tamahori, after several inauspicious big-budget Hollywood efforts he returns to his humbler roots with a bang. He fills the picture with raw energy, shocks us with some brief scenes of torture and killing (particularly in a party scene when he literally disembowels one of his father’s cronies), and—in concert with cinematographer Sam McCurdy and editor Luis Carballa—gives the film overall a surging, propulsive feel that carries one along even over the softer spots.

Most of those involve Uday’s preferred mistress Sarrab (Ludivine Sagnier), who quickly develops a liking for Latif—something he reciprocates, with dangerous consequences for them both. (After all, Uday’s “handler” Munem, played with a sophisticated air by Raad Rawi, warns Yahia not even to look at Uday’s women.) That leads not only to a curious triangle that recalls “Notorious” a bit, but to a final reel that, in all honesty, stretches credulity to the breaking point, involving as it does a hair-breadth escape, betrayal, and an assassination attempt in which one of the regime’s brutal henchmen abruptly shows signs of a conscience—or at least a choice to repay a debt.

This romantic angle frankly slows things down, and Sagnier, lovely as she is as a femme fatale, can’t really pull it off. But one supposes that an unremitting focus on the Uday-Latif relationship would have been too rough for many viewers to endure.

As a technical exercise “The Devil’s Double” is pretty impressive, with McCurdy’s widescreen images capturing the dusty brown ambiance of Iraq and the process shots in which Cooper appears with himself seamlessly rendered. All the behind-the-camera work—Paul Kirby’s production design, Charlo Dalli’s art direction, Caroline Smith’s sets and Anna Sheppard’s costumes—are top-drawer, and Christian Henson’s score blends modernistic touches with Middle Eastern touches, is also a plus.

So while “The Devil’s Double” might not make the grade in strict historical terms, it works more often than not as an action drama contrasting a demented villain and his right-minded stand-in.