If you were inclined to paranoia — if, like Dr. Leo Lieberstein, the narrator of “Atmospheric Disturbances” (Farrar, Straus and Giroux, 256 pages, $24), you detected portents in the most apparently banal details — your imagination might well seize on the large number 49 that appears on the cover of Rivka Galchen’s debut novel. Isn’t this an obvious allusion to Thomas Pynchon’s “The Crying of Lot 49,” which, like Ms. Galchen’s book, concerns the discovery of a secret conspiracy that may not actually exist?

Thinking like Leo, you might pursue the connection until it starts to appear everywhere. Oedipa Maas, the heroine of Mr. Pynchon’s novel, becomes aware of the existence of the Trystero, an ancient underground postal service, thanks to a graffito in a bathroom. Leo, a middle-aged psychiatrist, becomes aware that the Royal Academy of Meteorology is actually the front for a secret society that controls the weather, thanks to a mysterious diagram in a meteorological journal. The Trystero conducts a centuries-long war with Thurn und Taxis, its rival in mail delivery; the Academy’s job is to combat the 49 Quantum Fathers (thus that numeral on the cover), its rivals in weather control, who unleash destructive storms to further their evil ends.

Is “Atmospheric Disturbances,” then, just a rewriting of Mr. Pynchon’s postmodern classic? In fact, with the remorseless logic of insanity, you might conclude that it is precisely the differences that demonstrate Ms. Galchen’s constant preoccupation with her model. Mr. Pynchon’s protagonist is a woman, Ms. Galchen’s a man. Mr. Pynchon’s story takes place in Southern California, Ms. Galchen’s on the Upper West Side of New York. (Some important scenes take place in the Hungarian Pastry Shop on Amsterdam Avenue, “warm and humid, like a room for leavening.”)

Most important, where Mr. Pynchon’s real interest is in society and its power structures, making his novel essentially a satire, Ms. Galchen’s is in love and relationships, making her novel a psychological study. From this generic distinction follows the most important difference of all, and the one that makes “Atmospheric Disturbances,” for all its wit, a much more conventional book than “Lot 49.” With Oedipa Maas, the reader is genuinely never sure whether her conspiracy theory is simply paranoid, or whether she has stumbled on the hidden key that might show the chaos of history to be a kind of order. The more tantalizing the uncertainty, the more compelling is Mr. Pynchon’s portrait of a world so disordered that only the overdetermination of the paranoiac can make it right.

With Leo Lieberstein, on the other hand, it is clear from the beginning that we are dealing with a lunatic. Only for the first few pages does the reader wonder whether Leo is in fact correct when he insists that the woman living in his apartment — the woman “who looked exactly like my wife,” Rema, who is carrying Rema’s purse and talks with Rema’s Argentinian accent — is not actually Rema, but a diabolically clever impostor. “Same everything, but it wasn’t Rema. It was just a feeling, that’s how I knew,” he explains on the book’s first page, and on the last he is still sticking to his guns: “I can only ever love the original Rema.”

This central mystery is quickly defused, however, as we see Leo’s suspicions build to a baroque floridity that can be nothing but madness. Ms. Galchen designs her narrative so that we are always able to see the little fragments of reality that Leo incorporates into his paranoid designs. The central conceit of the weather war is given to him by one of his patients, the schizophrenic Harvey, who believes that he is one of the Royal Academy’s designated climate-changers. In what looks, in retrospect, like Leo’s first departure from reasonableness, he allows Harvey to believe that he, too, is an agent of the Royal Academy, hoping that he can at least convince Harvey to do his weather work in the New York area. In order to make this lie convincing, he finds a list of the fellows of the real Royal Academy and seizes on one — Tzvi Gal-Chen — as his alleged source for Harvey’s instructions.

By giving the elusive Tzvi, who never actually appears in the novel, a version of her own name, Ms. Galchen means to complicate her novelistic game, but the actual effect is to simplify it. Every time we read the name — and it appears more and more often as Leo starts to believe his own lie, convincing himself that Tzvi holds the key to Rema’s disappearance — we are reminded of the fictionality of Ms. Galchen’s world. “Gal-Chen” is like the author’s wink to the reader, delivered over the heads of the characters, reminding us that after all this is just a novel, a made-up story.

But the novel’s whole convoluted plot is justified only because it is supposed to make us question reality, and the signs by which we decide what is real. “If one wishes to be a true scientist,” Leo reflects, “then one must be willing to accept, to engage, even to pursue further the most unwelcome and confounding data. One must be willing to make discoveries that shatter one’s most deeply held beliefs.” By this logic, it is precisely Leo’s willingness to entertain mad ideas that proves he is sane. “I didn’t come up with this craziness,” he pleads later in the novel, “it came to me, not from me.” Pushed far enough — as it is in some stories by Borges or Kafka — this chain of reasoning can plunge the reader into a genuine metaphysical uncertainty. Ms. Galchen, however, never feels that much in earnest: With her elaborately researched digressions on meteorology and her metafictional jokes, she is too much in control of her story to let it menace her, or the reader.

By the same token, while Leo is an unreliable narrator, Ms. Galchen takes care to mute the potential havoc such a narrator can cause. Unlike the genuinely frightening narrators we meet in Dostoevsky or Hamsun, Leo is reliably unreliable — he is always wrong about reality in just the same ways, and so we are always able to correct for his biases, to see what is “really” happening in his fictional world. We never doubt, then, that the woman who behaves toward Leo just as a loving wife would — first offended by his coldness, then concerned by his unpredictability, and finally devastated and terrified by his complete irrationality — is in fact his loving wife.

Ms. Galchen relies on this double optic for her most moving effects, allowing the reader to see that it is just when Rema appears least “like herself,” to Leo, that she is most authentically herself. Take the scene, two-thirds of the way through the novel, when Rema, having pursued Leo to Buenos Aires, finally forces him to explain the “reasons” for his delusion. “Tell me,” she asks, “how am I not like Rema?” “For example,” he replies, “she’s more emotional than you are. And more nervous.” Of course, it is only because she finds herself on such treacherous ground that Rema is acting so exaggeratedly calm. Later on, when Rema is pushed too far and erupts into tears, that, too, will become grist for Leo’s mill: “I don’t know if you’d call her cry a sad cry,” he cavils, as though he has trapped the impostor in a piece of bad acting. “I suppose one might even call it a sob, but more of a distressed sob than a devastated one.”

It is on this level, the level of psychological realism rather than postmodern invention, that “Atmospheric Disturbances” succeeds, and where Ms. Galchen displays her real gifts as a writer. As we come to learn, in a series of dropped hints, the real story of Leo and Rema and their marriage, it becomes clear that the particular form of Leo’s delusion is anything but accidental. An older husband, a young wife with a mysterious past, a pregnancy that miscarried, dead fathers, and estranged mothers — these are the ordinary but powerful elements from which Leo concocts his fantasy about love and abandonment.

Finally, the “replacement” of Rema starts to look like Ms. Galchen’s metaphor for love itself. When Leo protests, “I can only ever love the original Rema,” he is not just voicing a delusion, but describing the paradox of commitment, which is passion extended through time. What would “Atmospheric Disturbances” look like, I wonder, if Ms. Galchen had devoted herself to this genuine human mystery, and dispensed with all the book’s gaudy, trendy, unnecessary paraphernalia?

akirsch@nysun.com