It is soon after the turn of the century. The reclusive American author Cormac McCarthy is taking a trip with his youngest son, John. He and his third wife are estranged, and share custody. It is early in the morning -- McCarthy does not sleep well -- and he rises from his bed, moves to the motel-room window and looks outside. The first rays of sunlight are breaking across the rocky landscape. He looks first at his son asleep in bed, then through the glass pane, gazing at a world he has populated with a ragtag band of misfits during his 40-year literary career, and he wonders what that world will hold for his son once he is gone; McCarthy is in his seventies, while his son has yet to enter his teens.

So began the author's journey towards The Road, his 10th novel, published in 2006, and the third to attract a Hollywood adaptation. The film, directed by the Australian John Hillcoat and starring The Lord of the Rings trilogy's Viggo Mortensen, opens this week. McCarthy unfolds a desolate, foreboding narrative, set in a post-apocalyptic world where an unnamed disaster has brought civilisation crashing down. Against this backdrop, the author unravels the story of a father and son who journey across an ash-strewn wasteland in a bid to reach the sea and possible salvation, picking their way past frozen corpses, starving survivors and roaming gangs of cannibals. As in his previous novels, McCarthy conjures a realm riddled with horror.

"My producer was able to option The Road because the studios were terribly freaked out by it," Hillcoat begins, with a wry smile. "They didn't want to have anything to do with it, so we got it as an unpublished manuscript. But none of us realised how it was going to grow, because what happened flies in the face of the studios' reaction." Upon publication, the book went on to win a Pulitzer prize and, even more important in commercial terms, earned Oprah Winfrey's seal of approval via her televised Book Club. Up until this point, McCarthy had yet to engage with a mainstream audience. He has never sought commercial acclaim and throughout his long career has regularly opted to live on the poverty line, letting marriages and relationships fail, rather than compromise his integrity.

The Road now had a powerful patron, however, and Oprah's recommendation saw the book reach out to a country fretting about its future and encouraged to seek out the message of hope and courage beneath The Road's austere exterior. "Looking at the bleakness in the book is like looking at the background and missing the point," Hillcoat says. "The studios couldn't actually see that they should have loved this story. It is a love story between a father and his son. It is about hope." He smiles. "But I guess it does lack a bit of comedy."

The fact remains that translating McCarthy's novels for the screen is a complex task. For a start, judging by the state of the publishing market, he shouldn't really be a bestselling author at all. Hewn from the bedrock of the Southern gothic tradition, his novels invariably traverse an inhospitable landscape, defined by concentrated natural observation and a raw and brutal realism. His apocalyptic visions rarely feature women, and he doesn't write about popular themes such as sex, love affairs or domestic intrigue.

His characters are usually misanthropes -- vagabonds, robbers, murderers, even necrophiliacs -- eking out a feral existence on the margins of society, shuffling around in the untamed backwaters of Tennessee or loping through the vast emptiness of the Texan desert. Death walks with them, executing his labour with a ready violence and an unremitting regularity. "There's no such thing as life without bloodshed," McCarthy said during a rare interview in 1992. "I think the notion that the species can be improved in some way, that everyone could live in harmony, is a really dangerous idea."

"He's not an easy writer to adapt, no," Mortensen concedes. "I love his work. I've read all his books, although this one I read as a script first, and I found it strangely affecting. It's not a gloss; it's very grounded in reality, in a journey that has a lot of soul-searching and suffering. It drives you on. You know where you are going, but you can't stop paying attention. It's like someone has done something that really gets to you. It can't possibly end that well, but it's such a clean story, as compared to so many of his books, especially Blood Meridian. It's also very honest and directly inspired by his relationship with his own son, which adds something. Plus, we've got the right director."

On the evidence of his last directorial outing, the flyblown 2005 Australian frontier tale The Proposition, Hillcoat's appointment looks a sage choice. Written by the singer Nick Cave, The Proposition echoes with a McCarthy-like refrain, recalling above all the author's epic, sonorous and truly savage Blood Meridian, a tale inspired by real-life events, tracking a pack of gore-stained scalp-hunters in the 1849-50 border wars. One reviewer dubbed McCarthy's opus "the bloodiest book since The Iliad".

Hillcoat smiles. "I think The Proposition was undoubtedly inspired by Blood Meridian," he says. "I tried to get the rights for that book. What I loved about it was that it showed the frontier in a really fresh light -- all frontiers are savage and, whether it's the indigenous culture or the occupying force, they bring out extreme behaviour. It's such a primeval conflict, as if McCarthy tried to write Heart of Darkness for America."

A big-screen version of Blood Meridian has long been mooted -- both Ridley Scott and Todd Field have been linked to a recent project -- but it will prove a curious challenge for any director brave enough to take it on. The existing adaptations of McCarthy's work have veered towards his more easily navigable novels. All the Pretty Horses, for example, the first of his films to find life on screen -- Billy Bob Thornton directing Matt Damon in 2000 -- proved uncharacteristically sweet-natured, infused with a bright innocence and simplicity. Thornton's film version, however, failed critically and commercially. The story goes that the producer Harvey Weinstein forced him to chop his 3½-hour final cut by a full third, leaving Damon to lament: "You can't cut out 35% and expect the same movie."

The Coen brothers' translation of No Country for Old Men had a happier outcome -- the film won four Academy Awards last year, including best picture -- although here the directors were aided, no doubt, by the arena in which the story plays out. Their central character is an unsettling sociopath, but McCarthy casts him in a modern, everyday world, thereby sparing the audience the cruel violence so often meted out in his wilder, more unforgiving landscapes.

Hillcoat, however, is shorn of that luxury, McCarthy bequeathing him his most dread landscape yet, a world devoid of life and colour, yet haunted by unspeakable terrors that transgress moral boundaries. The book might stand as the author's most personal novel, dealing with the relationship he cherishes above all others, and is thereby imbued with an unusual tenderness, yet it remains littered with harrowing incident, not all of which has transferred into the movie.

With the powerhouse producers Harvey and Bob Weinstein bankrolling the film, one suspects that Hillcoat, like Thornton, was asked to edit his final cut heavily. After all, while it's not a summer movie, the Weinsteins don't want to alienate the Oprah-audience with an overly distressing film. "You mean the baby on a spit?" Hillcoat asks when I inquire about the producers' take on the story's more grisly moments.

He is referring to a scene from the book in which the father discovers the headless body of an infant roasting over a fire. Infanticide is not uncommon in McCarthy's novels -- Outer Dark contains a chilling moment -- but the scene fails to surface in Hillcoat's film. "We made a choice about that," he offers. "We shot the scene, and it worked. But I wanted to get rid of it because, when you're adapting a book, everything becomes very physical. Reading a book, it is internalised. When you have that baby on the spit, strangely enough it takes away from the father and son's development in their journey."

As well as tempering the visceral horror, Hillcoat's retelling also fleshes out the character of the father's wife (played on screen by Charlize Theron), to whom McCarthy refers only occasionally in the book. "People talk about the expanded role of the wife, but it's not that much," Mortensen says. "It's more the fact that you see her, and you see how she feels, which is really very rational. She can see that people are going to rape them, kill them and eat them, so there's no point in going on. Yet the man wants to keep going -- he can't say why. Sure, there are people who eat their children, which is something you see in the book. You don't see that in the film, although it is implied, and I don't think that its absence detracts from the film."

McCarthy himself was tempted to the film set, bringing John with him. "I spoke to him before we started shooting, and we spoke about our sons and being dads," Mortensen continues. "It was interesting to see his dynamic with his son. It reminded me of the book. They have a very streamlined way of speaking to one another. They're clearly very close. When Cormac came to visit, we were shooting the sequences by the sea. He looked at what we were doing and just smiled, and said, 'That's exactly how I imagined it.' I thought, 'Well, that's good enough for me.'"