The violence that animated his great Western novels has been superseded by a flash of nuclear annihilation, which also blasts away some of what we expect from the reclusive author's work. With this apocalyptic tale, McCarthy has moved into the allegorical realm of Samuel Beckett and José Saramago -- and, weirdly, George Romero.

The novel opens on a world that seems to have been demolished by the psychopaths of McCarthy's earlier fiction, as though the Judge from Blood Meridian had graduated from shotguns to atomic bombs and vented his spleen upon the entire planet. It's a shift that transforms not only the physical landscape, reduced now to barren plains of ash, but the moral landscape as well. The fear of dying, so prevalent in McCarthy's previous novels, is balanced here by the fear of surviving: "Creedless shells of men tottering down the causeways like migrants in a feverland. The frailty of everything revealed at last. Old and troubling issues resolved into nothingness and night."

The Road ( Knopf, 241 pp., $24) follows two of the last people on Earth, an unnamed man and his young son, as they walk through an incinerated wasteland foraging for food and hiding from gangs of starving cannibals. "The nights now only slightly less black," he writes. "By day the banished sun circles the earth like a grieving mother with a lamp." This marks a significant departure for McCarthy, but it's hardly a departure for apocalyptic fiction and film, which have trafficked in these dark visions for decades. Of course, McCarthy has borrowed from lowbrow forms before. Most of his works are Faulknerian transformations of dime-store Westerns; his first modern-day novel, last year's No Country for Old Men, wore the worn costumes of a drug-crime police chase.

Without its rich voice, The Road would read like a remake of "Night of the Living Dead." Indeed, as if to acknowledge that debt, the man remembers his late wife saying, "We're the walking dead in a horror film." More than once, the little boy warns his father they shouldn't go into an abandoned house, but then -- no, stop! -- they go in anyway. There are also the requisite touches of gallows humor: the delicious taste of the last Coke on Earth, the only writing that survives worldwide destruction being a billboard that reads: "See Rock City." And finally, the one-dimensional horror-flick women: Most middle-school boys have a more nuanced understanding of the opposite sex than McCarthy demonstrates in his fiction, and he does nothing to alter that impression here.

But even with its flaws, there's just no getting around it: The Road is a frightening, profound tale that drags us into places we don't want to go, forces us to think about questions we don't want to ask. Readers who sneer at McCarthy's mythic and biblical grandiosity will cringe at the ambition of The Road. At first I kept trying to scoff at it, too, but I was just whistling past the graveyard. Ultimately, my cynicism was overwhelmed by the visceral power of McCarthy's prose and the simple beauty of this hero's love for his son.

The novel is made up of several hundred isolated moments, scraps of dialogue and flashes of action. Here's a typical one that could appear anywhere in the book:

"The land was gullied and eroded and barren. The bones of dead creatures sprawled in the washes. Middens of anonymous trash. Farmhouses in the fields scoured of their paint and the clapboards spooned and sprung from the wallstuds. All of it shadowless and without feature. The road descended through a jungle of dead kudzu. A marsh where the dead reeds lay over the water. Beyond the edge of the fields the sullen haze hung over the earth and sky alike. By late afternoon it had begun to snow and they went on with the tarp over them and the wet snow hissing on the plastic."

These remarkable passages, like a succession of prose poems, are marked by a few flashes of terror, but we're never forced to gorge on the gore that McCarthy's most devoted fans celebrate. There's only a glimpse of the civilization-ending catastrophe itself, which took place years ago, just before the boy was born: "A long shear of light and then a series of low concussions." Afterward this single haunting vision of the early days: "People sitting on the sidewalk in the dawn half immolate and smoking in their clothes. Like failed sectarian suicides. Others would come to help them. Within a year there were fires on the ridges and deranged chanting. The screams of the murdered. By day the dead impaled on spikes along the road."

These glimpses are metered out carefully in a way that only increases the sense of terror. It's the constant potential for carnage that energizes the story -- the hell that can be spotted in the flash of lightning, a baby on a spit roasting over an open fire.

Among his thinly plotted novels, The Road is McCarthy's most thinly plotted of all, as there's literally nowhere to go, no sense in going, just the inexorable impulse to move. The plot, such as it is, comes down to this father's existential need to keep his son alive and hopeful in a world that offers no life or hope. Day after day, month after month, they're starving and freezing, pushing along a cart with the few provisions they scavenge from decrepit homes looted bare years ago. "The boy was all that stood between him and death," McCarthy writes. "He saw for a brief moment the absolute truth of the world. The cold relentless circling of the intestate earth. Darkness implacable. The blind dogs of the sun in their running. The crushing black vacuum of the universe."

But against that lifeless state, the man clings to a raw faith in his mission: "My job is to take care of you," he tells his son. "I was appointed to do that by God. I will kill anyone who touches you." With everything scraped away, the impulse to sanctify, to worship, to create meaning remains. "All of this like some ancient anointing," the man thinks after washing his son's hair in an icy dead lake. "So be it. Evoke the forms. Where you've nothing else construct ceremonies out of the air and breathe upon them."

Concurrent with keeping his son alive is the more metaphysical challenge of sustaining his son's innate goodness while forcing him to witness the corruption of all moral behavior. "Are we still the good guys?" the boy asks in moments of confusion and shock. His father insists they are. "This is what good guys do," he tells him. "They keep trying. They dont give up." Why, then, his son asks, won't he help the stragglers they run across instead of running from them or shooting at them? "We should go to him, Papa. We could get him and take him with us. . . . I'd give that little boy half of my food." How to explain the necessity of abandoning others to certain death (or worse, in one particularly terrifying scene) while maintaining that they're "the good guys," the ones "carrying the fire"?

Under these singularly bleak conditions, the boy's nature -- his impulse to help, his anxiety about stealing others' food -- is, of course, naive. But even when fighting for their lives, his father knows that it's a naiveté inspired by the boy's goodness that makes their fight worthwhile, that allows him to resist the age-old temptation "to curse God and die."

The encounter that illumines the final moments of the novel will infuriate McCarthy die-hards who relish his existential bleakness, but the scene confirms earlier allusions that suggest the roots of this end-of-the-world story reach far past the nuclear age to the apocalypse of Christian faith. The book's climax -- an immaculate conception of Pilgrim's Progress and "Mad Max" -- is a startling shift for McCarthy, but a tender answer to a desperate prayer. ·

Ron Charles is a senior editor of Book World.