The sadism of Uday Hussein, Saddam’s estranged elder son who tortured Iraqi Olympians and served three months in a private prison for murdering his father’s closest confidante, is documented well enough without The Devil’s Double.

Yet Lee Tamahori’s adaptation of the tell-all by Latif Yahia, who reluctantly served as Uday’s body double before fleeing Iraq in 1991, isn’t merely the lurid chronicle of a lunatic son of privilege, but also of an escalating battle of wills between a madman and his disapproving sidekick.

Both are played by Dominic Cooper, in a role that establishes him as a formidable young talent as adept playing the straight man as the tyrant unhinged. The big problem with Double, which attempts to channel the same kinetic energy that made Brian De Palma’s Scarface such a memorable portrayal of an addict undone by his appetites, is Latif’s irredeemable blandness.

The drama is strictly one-note: Uday is a monster, hungry for power, money, drugs and women. He takes what he wants, and who’s to stop him? Saddam, presumably, though the late dictator remains distant from his son, occasionally making cameo appearances to register his contempt for junior’s excesses.

Latif, on the other hand, witnesses enough of Uday’s bad behavior – the abductions of teenage girls, the murders, the beatings and the near-constant binges – that he comes to see death as a welcome alternative. A reluctant beneficiary of Uday’s riches and opulent lifestyle, he is seemingly incorruptible, even when handed the keys to the castle.

It’s easy to sympathize with Latif and Uday’s exasperated mistress (Ludivine Sagnier, of A Girl Cut in Two), who are repelled by the maniac but too terrified at first to defy him. Befitting the irreproachable hero Michael Thomas’ script imagines him to be, Latif eventually grows emboldened by his disgust. Indifferent to preserving his own devalued life, he is free to defy his master.

When he does, Double giddily liberates itself from plausibility, in a made-for-Hollywood final act replete with shoot-outs, double-crosses and revenge. Whether it stays true to Yahia’s novel – inspired by real events, but hardly constrained by them – is beyond me, and probably beside the point.

What is the point, exactly? Lacking any real insights, Double is a thriller pure and simple, borrowing gravity it never really earns from the pages of recent history. Its greatest asset is Cooper, whose high-wire act is impressive to behold but somewhat compromised by the movie’s obvious limitations.