“What Belongs to You,” by Garth Greenwell. (FSG)

“What Belongs to You” whispers like an incantation of desire. But even as Garth Greenwell’s novel sweats with lust, his prose keeps that heat contained in the crucible of remorse.

Although this is a debut novel, expectations have been running high. “What Belongs to You” grew from a lauded novella called “Mitko.” And Greenwell’s literary criticism in the New Yorker and the Atlantic demonstrates an unusually keen and insightful mind. That promise is fully realized here in the dark magic of these pages.

The action, restrained as it is, takes place in modern-day Sofia, the capital of Bulgaria, a city depicted as rotting in its own history. With few opportunities and a stagnant economy, those who can leave, do; everyone else wallows in hopelessness spiked with wry humor. Greenwell taught English there at the American College, and he borrows the broad outline of that experience as the basis for his unnamed protagonist, who has picked up a working fluency in Bulgarian, but few friends.

The novel opens with a descent — physical, ethical and aesthetic — from which the narrator won’t rise for several years. Searching for anonymous sex in the bathrooms under the National Palace of Culture, he comes upon a rakish man working the stalls, “cordial and brash, entirely public in that place of intense privacies.” With broken phrases and lewd pantomime, they introduce themselves. He’s Mitko: “tall, thin but broad-shouldered, with the close-cropped military cut of hair popular among certain young men in Sofia, who affected a hypermasculine style and air of criminality.” Although the narrator had no intention of hiring a prostitute, he almost immediately brushes aside his pride and hands over cash for what he wants. When Mitko disappoints him, with a charming smile, it’s not the end of their commerce — or their increasingly fraught friendship.

“I’ve never been good at concealing anything,” the narrator says, “the whole bent of my nature is toward confession,” and what follows in this pithy novel is, indeed, a confession. But not primarily a sexual one. Although those encounters are described with raw detail, the narrator’s deliberate disrobing of his own psyche feels even more intimate. In Greenwell’s poetic sentences, emotional fearlessness is mated with extraordinary sensitivity to the tremors of regret.

Over the next few weeks, the narrator meets with Mitko repeatedly and then, recklessly, brings the young man to his apartment. As much as he desires Mitko’s trim body, there’s something equally irresistible about his disruptive personality. “Never before,” he writes, “had I met anyone who combined such transparency (or the semblance of transparency) with such mystery, so that he seemed at once overexposed and hidden behind impervious defenses.”

What develops is a mutually parasitic relationship that can’t end well. With his seductive magnetism and easy camaraderie, Mitko insists they’re friends, even as he trades sexual favors for cash and Internet access. The narrator, meanwhile, sustains the illusion of his own affection and beneficence, in essence paying for the privilege of being an American savior, wavering between the thrill of passion and the “acidic sense of entrapment.” He allows himself to imagine that he can extract “something like nobility from the mawkishness of desire, the sense that stray meetings in dark rooms or the shadowy commerce of my own evening could burn with genuine luminosity, rubbing up against the realm of the ideal, ready in an instant to become metaphysical.”

During several subsequent meetings, the narrator continues to probe his own motives, peeling back the layers of his pretense to expose what need is really motivating him. Some flights of memory begin merely as daydreams but then gradually coalesce around scalding realizations — none more so than an extended recollection of the time his father discovered his son was gay. “His look entered me and settled there and has never left,” he writes. “It rooted beneath memory and became my understanding of myself, my understanding and expectation.” It’s the kind of lacerating scene that reminds us that our liberal era is still strewn with wounded survivors of homophobia, adults nursing injuries too deep to see, too deep to heal.

This is a novel of aggressive introspection, but Greenwell writes with such candor and psychological precision that the effect is oddly propulsive. The sustained tension between the narrator and Mitko will remind some readers of Damon Galgut’s “In a Strange Room,” which was a finalist for the 2010 Man Booker Prize. But that novel’s tone was more mannered and its style so self-consciously profound. With a similarly subtle plot charged with erotic energy, Greenwell provides a richer experience, and his constantly burrowing sentences are polished to a deep luster.

The narrator’s alienation is emphasized even by the novel’s attention to foreign phrases, the little gaps that open up between imperfect translations. How appropriate that his name is unpronounceable in this country. He remains, likewise, unmanifested, like some rootless spirit. “I know they’re all I have,” he admits, “these partial selves, true and false at once, that any ideal of wholeness I long for is a sham.”

In the end, a novel like this can’t offer any resolution except its perfect articulation of despair that anyone with a heart will hear.

Ron Charles is the editor of Book World. You can follow him on Twitter @RonCharles.

What Belongs to You

By Garth Greenwell

Farrar Straus Giroux. 194 pp. $23