Once the credits roll on “The Devil’s Double,” there’s not much to do but shrug. There’s no denying that Dominic Cooper’s dual performance is an impressive feat, but it’s also the gimmick the film is built on.

Director Lee Tamahori makes the fatal mistake of hoping Cooper would be enough to carry the film and overshadow the muddled characterization, wildly uneven tone and repetitive plot. Unfortunately, this isn’t the case.

Set in Iraq around the time of the Gulf War, “The Devil’s Double” tells the true story of Latif Yahia (Dominic Cooper), an Iraqi who is drafted into a peculiar kind of military service and disguises as the double of Uday Hussein (Cooper), Saddam Hussein’s entitled, psychopathic heir.

From the beginning, Yahia thinks the younger Hussein is scum, and Uday is delighted at the concept of having a new toy that looks just like him. The relationship between the two, however, never really develops beyond that because both characters lack nuance. Too much of the film is devoted to Yahia brooding while Uday commits excessively violent crimes. Cooper does his best to keep Latif interesting, but Cooper steals the show out from under himself as his Uday Hussein becomes absolutely terrifying. His subtle lunacy quickly blossoms into full-on cartoonish menace. Cooper’s best moments as Yahia are when the deadly calm soldier slips into an imitation of the energetic Uday.

The film’s tone is also a significant issue. It’s unclear what the film is trying to be or say. Opting to wallow in colorful brutality, reminiscent of “Scarface,” in some moments and honing on how horrific Uday’s deeds are in other scenes, the product is a wonky example of light, frothy entertainment about bloodcurdling subject matter.

That isn’t to say “The Devil’s Double” isn’t stylish though. Tamahori makes the luxury of Iraqi royalty sleek and seductive, lingering on the fancy clothes, fast cars and affluent lifestyles before slapping an uglier sheen on things to show how Uday treats his subjects.

Of all the missteps in “The Devil’s Double,” its handling of the source material is the biggest. Characters outside of Uday or Yahia are barely developed — it’s as if they were never there to begin with. And a quick scan of Yahia’s Wikipedia page shows that a final act based on what really happened would have been miles better than how the film wraps up.

“The Devil’s Double” is too problematic to recommend with any conviction. It’s too reliant on the central gimmick and an impressive set of dual performances, but Cooper earns every accolade he gets for this film. He’s a strong performer and does great work here even without much of a screenplay to work with. While the film itself is spotty and falls apart under scrutiny, it’s hard to say that Cooper’s performance doesn’t save the film from being a complete and utter failure. Instead, it will be regarded as the “Scarface” wannabe that launched the career of this promising young actor.