Many critics had figuratively (or indeed literally) packed their bags before the last film screened in this year’s Cannes competition. Predictions had been made. A few overall assessments of the race for the Palme d’Or had been published.

It took only a few minutes of Lynne Ramsay's stunning You Were Never Really Here - a brutal thriller set largely in New York's meaner streets - before we found ourselves wondering how anyone could have been so foolish.

Rumours to the effect that the film was not quite finished had, perhaps, caused a few to talk down its potential. Sure enough, You Were Never Really Here is not in a completed state. There were no end credits on the print screened in the Debussy Theatre and, at the press conference, Ramsay explained they were still editing.

But it stands out as the most aesthetically uncompromised picture in the main strand. As she proved in Morvern Callar and We Need to Talk About Kevin, Ramsay is among the best British directors of her generation. And this is pure Ramsay.

You Were Never Really Here follows a familiar enough shape. Based on Jonathan Ames's 2013 novella, the picture stars Joaquin Phoenix as Joe, a private operative - formerly a US soldier - who finds much of his time taken up rescuing the victims of sexual slavery. A US senator hires him to recover his daughter and punish those who put her through hell. The first death triggers a veritable carnival of slaughter.

So much stands out here. There is nobody better than Phoenix at conveying numbed psychosis and, more bearded than a retired buccaneer, he excels himself in his conspicuous tussles with those inner torments. He has the look of a man who is never more than five minutes away from processing bad news.

Ramsay expands Joe’s story in ingenious, disciplined fashion. The traumas he suffered serving in the army are dealt with in a brief ambiguous flashback that lasts little longer than three minutes.

His own childhood abuse is referenced in muttered shouts on the soundtrack and through a continuing need - apparently inspired by his dad’s bullying -- to wrap his head in cellophane. His sweet interactions with his elderly mother (Judith Roberts) admit just a little kindness into a cruel film.

Ramsay’s sound design has always been a great strength and, once again, she conveys as much through bumps, scratches and screeches as she does through images. (None of which is meant to undermine Thomas Townend’s stunning cinematography.) She is helped in her efforts by a typically brilliant angular score from Jonny Greenwood.

Ramsay doesn’t shovel on his chords, but the expressionistic sawing is there to heighten already breathlessly tense moments. There are few film-makers so adept at making visual and aural flesh of the internal. Much happens on the outside here: killings, abuse, fury. But much more happens on the inside.

Such stories have inspired countless Charles Bronson films. You Were Never Really Here is closer in tone to John Boorman's Point Blank (in its fanatic momentum) or Martin Scorsese's Taxi Driver (a near-maniac rescues a young girl).

Yet the film remains utterly its own singular beast. What really sets it aside is its breathtaking economy. You Were Never Really Here was listed at 95 minutes in the Cannes schedule. When it closed triumphantly after just 85 minutes, the audience had to pinch themselves before breaking into loud applause. There are multitudes in here, but not a second is wasted. It is a brash, noisy, violent picture, but it is also a subtle, intricate, thoughtful one.

Might Cannes finally give a second Palme d’Or to a woman? Don’t bet against it.