Baghdad, 1987. Saddam Hussein's gangster regime rules Iraq with rampant brutality, but the feared "royal family" must take precautions even so. Saddam employs "fidays," or body doubles, to impersonate him at public events, throwing potential assassins off track.

Iraqi army lieutenant Latif Yahia (Dominic Cooper), a schoolmate and close lookalike of Saddam's psychotic son Uday is ordered to perform the same service for the sadistic party boy. Latif is repulsed by "the Black Prince's" hair-trigger violence and sexual sadism, but Latif's life and his family's are on the line.

"The Devil's Double," inspired by Latif Yahia's true story, follows the upright soldier's bizarre prince-and-the-pauper story as he doubles for this Mideast Caligula. It is a ghastly, riveting, dazzling piece of work.

Director Lee Tamahori ("Die Another Day") takes this bizarre scenario over the top, and then over the top of the top. Modeling the story on coked-up '80s gangster thrillers, he turns the story into "Scarface, Iraqi Style." The film is a nightmare of opulent decadence, with vast mausoleum sets, hallucinatory discos, exotic cars and gold-plated automatic pistols. The gaudy spectacle implies a sick connection between unchecked political power and sexual depravity. Every frame shimmers with oppressive desert heat and danger.

Cooper (last seen as good-guy inventor Howard Stark in "Captain America") delivers a career-making turn playing both the decent, dignified Latif and his manic, homicidal lookalike, Uday. Cooper gives each role verbal and physical idiosyncrasies.

Uday has the hot-wired impulsiveness of a Bugs Bunny, and front teeth to match. But there's nothing funny about his capers. He's exhilarated by the idea that he can do whatever he likes (and he likes very bad things) without consequences. Latif has a military man's self-control and precise posture. He's smart enough to be frightened but courageous enough to be instinctively defiant.

The two men are so distinctive that we thoroughly enjoy Latif's ever-more-accurate imitation of his nemesis. "You are asking me to extinguish myself," Latif protests, yet Cooper's double turn is a flamboyant Roman candle of a performance. You'd think that Cooper's audacious Uday would overpower the story, but Cooper maintains a satisfying balance between the polar opposites. He is riveting every moment he's on the screen, which is practically every moment.

Uday's penchant for sexually degrading and killing any woman who catches his eye ultimately comes home to roost in very violent -- and, it must be said, satisfying -- fashion. Sic semper tyrannis. On second thought, make that sick semper tyrannis.