It’s been 16 years since Cormac McCarthy published his apocalyptic masterpiece The Road, won the Pulitzer, and then, having secured his place in literary history, apparently vanished into the mists. Now, at 89 years old, he’s returned with two new books: The Passenger, out now, and its companion novella Stella Maris, out in December. Together they form less a capstone to McCarthy’s storied career than they do a compelling if uneven coda.

Some of McCarthy’s most celebrated novels are page-turners, but that’s not on the agenda here. These books are built to stand apart from the reader, to withhold, to refuse to satisfy. You can almost feel McCarthy swaggering a bit as, with great skill and elegance, he chooses time and time again to frustrate any desire the reader might have for either narrative or story.

The Passenger and Stella Maris occur 10 years apart from one another, each told by a different sibling. The Passenger takes place in the 1980s and is narrated by Bobby Western, a taciturn tough guy who was once a race driver, is currently a salvage diver, and maintains a deep knowledge of theoretical physics. Stella Maris takes place in the 1970s and is narrated by Alicia Western, a diagnosed schizophrenic and math genius. Their surname is Western because that’s what they stand for: the western postwar world order, with all its prosperity and order and all its moral compromises. In The Passenger, Bobby is in love with Alicia, who is dead. In Stella Maris, Alicia is in love with Bobby, who is in a coma. Both maintain they never consummated their relationship, but McCarthy gives you just enough room to wonder if that’s the truth.

The official line from the publishers is that The Passenger and Stella Maris each stand alone, but don’t believe them. The Passenger would be maddeningly opaque without Stella Maris to elaborate on some of its most compelling plot threads, and Stella Maris would be dry as book binding without The Passenger to leaven its many philosophical arguments. Reading them separately would be a cramped and despairing experience.

Not that The Passenger is exactly a light read in and of itself. While it gestures at a pulpy thriller plot involving a passenger vanishing from a crashed plane and mysterious government agencies chasing Bobby Western down, McCarthy serenely declines to either solve or, indeed, provide real suspects for any of his mysteries. They seem to exist merely to create the paranoid murk through which Western (as McCarthy consistently calls Bobby) must dive as he encounters and has Socratic dialogues with a series of colorful characters.

With a trans woman, Western discusses the question of whether there is a God or a female soul. With a magician turned private detective, he talks about the tragedy of beauty. And with an absolute blank slate of a character — so blank it’s almost offensive, really, as if McCarthy’s staring us in the eye and daring us to call him on it — Western gets into the real issue of these two novels: the atom bomb, quantum mechanics, and the question of whether reality is knowable.

“It’s all right to say that the reason we cant fully grasp the quantum world is because we didnt evolve in that world,” Western explains. (McCarthy’s still doing his thing with leaving out apostrophes and quotation marks.) “But the real mystery is the one that plagued Darwin. How we can come to know difficult things that have no survival value.”

Western comes by his understanding of this mystery honestly. He and Alicia are the children of one of the makers of the atom bomb, born, like all the postwar west, to the knowledge that they owe their wealth and good fortune to an atrocity that might have stopped a bigger atrocity. Both of them got an education in physics from their father, and both of them are deeply aware of the implications of modern physics for reality: the way it shows us that reality does not match our understanding, that the universe is less stable and more eerie than we thought.

Western responds to this knowledge by briefly pursuing a career as a physicist before failing his subject: He decides he isn’t quite good enough to do really valuable physics. Alicia, meanwhile, decides to go into pure math before being failed by her subject: since math has no provable reality independent of the human mind, she decides it is not equal to solving the problem of what reality is. Alicia’s project is to try to hold the truth of what contemporary physics and pure mathematics tell her completely in her mind, and the implication is that either the effort has shattered her mind or that only a shattered mind could attempt to do so in the first place.

Alicia appears periodically throughout The Passenger. Her death by suicide opens the novel, and in flashbacks we see her conversing with her hallucinations: a raggedy carnival barker of a man she calls the Thalidomide Kid, with flippers instead of hands, and all his hangers-on. (These hallucinations, it must be said, are appallingly tedious.) She doesn’t take center stage, though, until Stella Maris, which is made up entirely of Alicia’s conversations with her psychiatrist in the last year of her life.

There is something pleasingly, shockingly bare about Stella Maris after the lushness of The Passenger’s rich, haunted atmosphere. The Passenger takes place in New Orleans in the summer, but Stella Maris is all cold, cold, midwest in the winter. Gone, too, are The Passenger’s showy and circuitous plotlines about the JFK assassination being a cover for the mob taking out RFK and secret caches of gold buried in a dead grandmother’s basement. In Stella Maris, McCarthy has stripped away all the flesh down to the bare bone, the part that he’s actually interested in talking about.

It turns out the bone is more theoretical physics and pure math, the cosmic questions they inspire, and the creative work entailed in thinking them through.

“I knew what my brother did not,” Alicia explains to her shrink. “That there was an ill-contained horror beneath the surface of the world and there always had been. That at the core of reality lies a deep and eternal demonium.” The inexplicable void at the core of quantum physics is the demonium.

Writing women has never been McCarthy’s strong suit, and Alicia doesn’t exactly hold up as a rich and three-dimensional character. Her voice is appealingly spiky, but she’s more philosophical construct than whole human being. Yet halfway through Stella Maris, it becomes clear that she’s also an avatar for McCarthy himself, and for anyone who finds their unconscious mind doing their creative work for them.

“The core question is not how you do the math but how does the unconscious do it,” she says. “How is it that it’s demonstrably better at it than you are? You work on a problem and then you put it away for a while. But it doesnt go away. It reappears at lunch. Or while you’re taking a shower. It says: Take a look at this. What do you think? Then you wonder why the shower is cold. Or the soup. Is this doing math? I’m afraid it is. How is it doing it?” (Punctuation original.) You can slot in writing for math in that paragraph without changing the meaning a jot.

Speaking of writing, it’s just as great here as you would expect. Sometimes I think the reason literary criticism got obsessed with evaluating prose as “sentences” over the past few decades is simply that McCarthy’s are so good. They rattle out at you like little bullets, mean and punchy and precise.

Here he is on what it means that our reality is dependent on our observations: “In the beginning always was nothing. The novae exploding silently. In total darkness. The stars, the passing comets. Everything at best of alleged being. Black fires. Like the fires of hell. Silence. Nothingness. Night. Black Suns herding the planets through a universe where the concept of space was meaningless for want of any end to it. For want of any concept to stand it against.” The rat-a-tat-tat of those terse and isolated clauses; the easy richness of the phrase “alleged being” against the showy imagery of hellish black fire and silent black planets: When you’re as good as McCarthy, you make it look easy.

Still, McCarthy is stingy with the pleasures of his prose. In this pair of novels, his most ravishing sentences tend to evoke horrors, either cosmic or personal. He is stingy, too, with the possibility of sweetness or joy. The only true tenderness in these novels comes from Alicia and Bobby’s incestuous love, which McCarthy treats as both redemptive and destructive.

Neither The Passenger nor Stella Maris is designed to be anyone’s gateway to Cormac McCarthy. They lack the visceral emotional intensity McCarthy can conjure at his best; they are pointedly spare and withholding. But taken together, they offer an intellectual experience that’s not quite like anything else out there, laced with the eerie beauty that only Cormac McCarthy can offer.