What else can you call it but star quality? It was that – that ineffable, incalculable thing that makes certain actors on film seem almost holy – which made Marilyn Monroe one of the icons of cinema, perhaps the icon. That, coupled with her untimely death, which meant Monroe never grew any older on screen, is surely why she endures even now, 100 years after her birth. Whether performing Diamonds Are a Girl’s Best Friend in Gentlemen Prefer Blondes, vamping in Niagara or throwing off sparkling dialogue in Some Like It Hot, Monroe seems to belong up there on the big screen – so much so that you might believe she never actually existed down here with us.

It’s Monroe’s last picture, 1961’s The Misfits, that shows the star was mortal after all. It begins in Reno, where Monroe’s out-of-towner Roslyn gets a quickie divorce from her absentee husband (Kevin McCarthy) before falling in with a group of local oddballs, among them an ageing cowpoke, Gay Langland (Clark Gable), and a buck-drunk bronco rider, Perce Howland (Montgomery Clift).

Together, this motley crew booze and drift through Nevada’s bars and rodeos towards the desert where, at the film’s climax, they search for the area’s last remaining mustangs to rope and sell for dog food – these majestic creatures having become, like the film’s characters, relics who have near-outlived their usefulness.

The director, John Huston, a sure hand with tales of self-destructive characters, gives The Misfits a gloomy air of impending finality, shooting in ever more desolate locations in soon-to-be outmoded black and white, and casting in the principal roles three stars who were all heading for oblivion. Among the brightest talents of their respective generations, Gable, Monroe and Clift all had what would soon prove to be fatally severe substance abuse issues. Only Clift would finish another film; Gable died of a heart attack just 12 days after The Misfits wrapped.

As if sensing that their time was up, The Misfits’ three stars act for their lives. Gable never conveyed greater pain than in the moment a smashed Gay howls uselessly into a crowd after his estranged children, while Clift was rarely as vulnerable as he is in the film’s expertly played phone booth scene, in which Perce calls up his mother, desperate for the love and approval she won’t provide.

It’s Monroe, though, who wrings her role for every last nuance. Roslyn was written for Monroe as a “gift” from Arthur Miller, The Misfits’ screenwriter and Monroe’s then-husband. As spousal gifts go, it’s a curious one: a part that casts Monroe as a woman who wants out of a miserable marriage (Monroe and Miller split shortly after The Misfits wrapped) and the most broken and lonely figure in a film full of them. In The Misfits, the almost otherworldly beauty and presence that in other films positioned Monroe as an elevated object of desire is used to make the actor appear fundamentally separate from everyone around her – in the world, but not quite part of it.

Roslyn is also a role, however, that Miller tailor-made for Monroe to show her previously unseen strengths as a performer. Having had ample opportunity to prove her ease and timing as a comic actor before making The Misfits, Monroe gets her most significant dramatic part in Roslyn, a character of real complexity and contradiction: impulsive yet timid, innocent yet world-weary, vivacious yet chronically sad. A student of the method, Monroe doesn’t just play the part ably, she goes deeper than what’s on the page; her eyes and energy throughout The Misfits suggest a constant interrogation of the scene, of every line. Monroe was never more alive on the screen.

The Misfits wasn’t supposed to be Monroe’s last film; she was due to resume shooting the ultimately unfinished romcom Something’s Got to Give, when, in the summer of 1962, she was found dead in her home from a barbiturate overdose, aged 36. That her final completed film suggests a generational star was capable of yet more only deepens the tragedy about this film: it should have marked the beginning of another phase of her career.

Still, as final roles go, Roslyn could be considered an apt one. Conceived by a writer who knew Monroe intimately, it’s a part that burrows beneath the image of “Marilyn Monroe, star”, and allows the actor to show that she knew what it was to be painfully, knottily human.

• The Misfits is available to rent or buy on Apple TV in Australia, the UK and the US. It’s also available to stream on Prime Video in the US. For more recommendations of what to stream in Australia, go here