Why on earth put this material in the hands of the Australian director of The Proposition (2005), the film that Nick Cave backed (and wrote); a bushranger western with a clawing sadism that makes Sam Peckinpah look restrained? Many wise heads thought highly of The Proposition, which has Guy Pearce as an outlaw who comes back to fight his nemesis, but which, just to savour atrocities, includes a scene in which the hero’s brother, a retarded boy, is whipped to death, with accompanying screams. The Proposition seemed to me like the kind of arthouse schlock that rides into battle with severed heads and genitals held on high as emblems of a ghastliness that can outstare realism, a cocaine-like fantasy of epic grandeur that sizzles and fizzles with a sort of adolescent poetry but lacks anything that might give it form and pressure.

It seemed like a match from hell, but it’s not. The Road is a good film of a powerful book on an unspeakable theme. Although it is not hard to comprehend Hillcoat’s affinity for the starkness and terribilità of the subject, the film of The Road displays an appropriate mixture of grotesquerie and restraint.

This impressive ‘Australian’ contribution to international cinema stars Kodi Smit-McPhee, the extraordinarily talented child actor who played Rai in Richard Roxburgh’s Romulus, My Father (2007), a radiant performance which was the finest thing about that film. The father in The Road is played by that superb actor Viggo Mortensen; Charlize Theron is a vivid presence as the wife and mother.

Joe Penhall’s script, an adept translation of McCarthy’s apocalyptic tale, should ensure that this improbable book by a literary writer who is also a popular writer should have a permanent hold on the collective consciousness, notwithstanding its unthinkable horrors.

McCarthy is one of those writers who, like Ian McEwan and Tim Winton in their ways, commands a much broader readership than the one purely interested in literary writing. In that respect, as in others, McCarthy is the heir of Hemingway, with a thundering command of action that enthrals, though his cadences are stately and artful and the feeling that runs through his books encompasses the pity and the terror and the tears in things. You begin reading All the Pretty Horses, which opens his Border Trilogy, thinking that you are experiencing the Platonic idea of escapist writing because you are enjoying a cowboy book for the first time since you were ten; only to discover that this is no reanimation of the delights of childhood. It is a Kindertotenlieder. But the momentum of the great entertainer is present in McCarthy, together with his transfigured double the dramatic artist. That’s why his books are not only made into films but into the kinds of films that highlight the books they derive from and enhance their prestige: Billy Bob Thornton’s film of All the Pretty Horses (2000) and the Coen brothers’ No Country for Old Men (2007).

In one sense, The Road presents the enduring Cormac McCarthy theme stripped bare of his yarn-spinning charm: it is the story of an innocent wandering a world that will not acknowledge the sanctity of childhood. The narrative excitement is acute because the slaughter of the innocent is all but inevitable. Behold the lamb of God whose flesh the malignant will eat.

As a novel, The Road achieves its catharsis through the figure of the boy, even though this is ‘black milk of daybreak’ stuff. Hillcoat’s film doesn’t have quite the same keening curve of catastrophe, but it remains moving and powerful, even as it walks through the ashes of the world. Mortensen is the father who, pained and anxious, travels endlessly with his boy after his wife – Theron golden and bitter in recurrent flashback – refuses to continue on a journey that she predicts will end in her child’s being raped and cannibalised.

The film, like the book, is made up of the nightmare journey through an America that has long ago entered the dark wood that leads to hell. The Road is a kind of Inferno-like buddy story, a film about a father and son, but one in which survival, the all-but-impossible goal, has replaced enlightenment, and where any Huck Finn-like lighting out for the territories will involve seeing the bonfires of human souls.

From the outset, the film skilfully establishes the moral gravity that underlines the horror-style narrative momentum. The father’s narration tells us that if God’s voice does not come through the child, then he never spoke a word. And so it goes as father and son move over the bleached and devastated landscapes of some rural Pennsylvania or Oregon of the mind, some Montana that may be coterminous with a world where men rove like wolves. Over and over the boy asks his father, ‘Are we still the good guys?’; over and over the latter, striving to protect him against the mercilessness of the world, wants to deny mercy to the passers-by who may be the enemy. When they meet the old man played by Robert Duvall, his eyes scarcely anything but the milk of cataracts, it is the boy who insists that he be fed. Wherever the boy goes he insists, with a matter-of-fact reasonableness that never dissipates the realism, that kindness must prevail, however much the rest of the world wants to destroy you.

The tension between this belief and the father’s willingness to kill for him, and die for him, constitutes much of the force of this scarifying biblical fable of a film. If the book maintains its air of catastrophe and the drumbeat of its drama, there are moments, sometimes sustained moments, when Hillcoat’s film loses itself in the melancholy of its elegiac landscapes and its evocation of the mournful beauty of a world that has become an abomination of desolation.

It is the hardest thing in the world to sustain drama in the face of ruination. To achieve it you need a director like Ingmar Bergman in the late 1960s; either his unrelenting sense of drama or the eye of genius for physical choreography that Steven Spielberg displayed in the desolation of the ghetto sequence in Schindler’s List or in the Normandy landing that opens Saving Private Ryan. Hillcoat can evoke the dumbfounded aspect of Goya’s parables of war, but not the unceasing eloquence.

None of this is to deny the fineness of what he does achieve or the formidable authority of Javier Aguirresarobe cinematography, so distressed and drained of the touch of nature that is meant to make the whole world kin but in this instance makes humanity itself red in tooth and claw.

The midwinter light of this film, the grey light in which its last rites are enacted, is ashen and awes the mind. The flashes of severed body parts are shown deliberately, momentarily, with considerable restraint. Theron’s characterisation – the wife who refuses to bear the unendurable – is without any hint of sentimentality. Mortensen as the good man, an Abraham striving to be decent in the face of atrocity but protecting his son like a tiger, has a superb quality of negative capability.

But it is Kodi Smit-McPhee’s film. Like a baby Dante, he traverses a world where it is almost impossibly hard to believe in the good, even though the ability to maintain the faith is the one justification for life. Smit-McPhee, who demonstrated in Romulus his ability to convey a world of inarticulate feeling through the wide stare of those beautiful eyes, is shot less lyrically in The Road, but his acting still takes the breath away. Everything about this film is serious, intelligent, heart-felt, but he sweeps its careful and devotional intensities into another dimension.

This marvellous performance gives the film the sort of haunted, apparitional quality it needs if the child’s goodness is to rise up against what is most savage and sinister in the leftover world. The boy’s sheer niceness carries the force of Christ’s summarising commandment. It is a remarkable feat on Hillcoat’s and Penhall’s part to realise this most difficult aspect of Cormac McCarthy’s very traditional vision. It is a vision of innocence, willing to risk anything, to walk absurdity’s tightrope, so that its voice, its still small voice, may be heard.

It is strange that a novel like The Road can win the Pulitzer Prize; stranger still that this local film, with music by Nick Cave, can be made. That a film bound to scare almost anyone can eventuate, with a first-rate cast using an Australian child actor of nearly limitless range and expressiveness, is also an indication of what might be possible in this country. Kodi Smit-McPhee’s performance is on a par with Anna Paquin’s in The Piano. He constantly alludes to a world of human feeling with a sublimity that dovetails with his childishness and makes most sophistication look footling.