Good actors and angry drunks — they keep you on your toes. Here, in a loose reworking of John Cassavetes’s Gloria, Tilda Swinton plays the furious, staggeringly tipsy Julia at full tilt. Someone describes this LA woman as looking like a giraffe. She does: her long legs and long neck gyrate awkwardly in search of booze and sex. But these are surface pleasures, the sort of thing often seen in portraits of sleazy living by slumming-it actors. The big surprise is that Julia the film and Julia the character offer so much more.

French director Erick Zonca is best known for the beguilingly bleak The Dream Life of Angels, which ends with a young girl’s suicide. He has been wrestling his own demons ever since, but seems to have found a release via Cassavetes’s overwrought American fairytale. The original tells of a hard-bitten, Mob-connected moll who finds redemption through an orphaned boy.

Sidney Lumet remade the story a few years ago with Sharon Stone and the result was cringeworthy. Zonca and screenwriter Aude Py have gone for an altogether different tack. Julia is no longer a victim of circumstances. Instead, motivated by greed and delusions of a fresh start, she grasps an opportunity to go on the run with a nine-year-old boy. He is no longer a victim of trauma, either — at least not until Julia comes along.

The perfectly cast Kate del Castillo, playing Julia’s Mexican neighbour and fellow alcoholic, Elena, gets the ball rolling. Elena asks Julia to snatch a boy, Tom (Aidan Gould), away from his rich grandfather, explaining, with tears in her eyes, that the boy is her son and that if Julia gets him to Mexico, she will be rewarded with a share of his inheritance. Elena’s anguish is palpable. So is her madness — sticky-sweet hysteria rolls off her in waves. Elena wants Tom, Julia wants money. Will either of these crazy women get what they desire?

As it happens, Julia manages to make off with the hapless boy and demand a ransom from his grandfather as she drives Tom towards Mexico, which is a miracle given her mental state — most of Julia’s big plans are interrupted by an urgent need to pass out. Swinton’s increasingly subtle performance soon has us laughing and gasping, all in the same breath.

Like most drunks, Julia is a congenital liar. She starts to reinvent Elena as a perfect mother. She also seems keen to reinvent herself, yet remains unreliable. Swinton doesn’t settle for a definitive self for Julia; she simply allows her character to see-saw in front of our eyes. The constant motion is hypnotic.

I wondered sometimes about her accent, but ever since The Beach Swinton has been cast by Americans as an American, and they should know. She missed out on the Best Actress prize at the Berlin Film Festival and it will be an outrage if her work here — so much more complex than her mannered turn in Michael Clayton — goes unacknowledged.

Gould deserves praise, too, for keeping up. We believe Tom is frightened of Julia when she throws him in the boot of her car. We believe that he believes what she tells him about Elena. That’s actually quite a jump, yet the young actor makes the transition look easy.

That he believes Julia’s blarney about his mother could, in another film, come across as too schmaltzy but throughout the pair’s adventures in the desert — and later Tijuana, Mexico — we’re ever mindful of Elena’s hysterics.

Zonca never gives us an easy ride. The film bumps and rattles and sometimes runs clean off the road. Towards the end our duo fall in among thieves and the plot turns slapdash and hurried.

Yet even this seems to work in the movie’s favour because it is entirely in keeping with the jittery, out-of-control mood.

Julia, by and large, is a tale of desperate opportunists, fugitive souls who survive by living on their wits, taking risks and making it up as they go along. It sometimes feels that a similar person is behind the camera as well as in front of it.

Does this glamorise alcoholism? I don’t think so. At one stage Julia’s only real friend, Mitch (Saul Rubinek), admits that he once hospitalised his daughter in a drunken rage. What Julia puts Tom through amounts to child abuse as well.

On the other hand, when Tom repeats his grandfather’s maxim that people who take drugs are “weak”, Julia’s blink of surprise speaks volumes. She knows it’s more complicated than that. By the end of the film, so do we.

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