At the start of the American Civil War, there were roughly 150,000 Jews living in America. Many fought, and many that did took the side of the Confederacy. Peter Charles Melman, a Long Island Jew, raised and educated in Louisiana, sees this as a curious anomaly and perhaps even a breach of faith: Why would one long-oppressed people take up arms to protect a system that oppressed another?

The Confederate Jew at the center of “Landsman” (Counterpoint, 318 pages, $24.95), Mr. Melman’s richly conceived but haphazardly constructed chivalric romance, is a young New Orleans delinquent named Elias Abrams — a thug, a hustler, a cardsharp, and a thief. But that’s all just circumstance, Mr. Melman insists: Abrams is practically a pacifist, or what passes for one in New Orleans, a gutter-fed romantic, a whoremonger with a heart of gold.

The child of an unmarried field laborer and indentured servant, Abrams had what Mr. Melman magniloquently calls an “earthen upbringing,” and has inherited his mother’s respect for southern soil and its tilling. As a farmer, his mother was fond of foreign plants, and was fervently committed to transplanting them into American earth. “There is no need,” she instructs Abrams, “to reject a plant when it does not succeed during the first years of its introduction to a particular climate.”

A noble sentiment, perhaps, but it makes for poor gardening, and in the nine years following her death, Abrams proves himself a remarkably stubborn transplant, refusing to lay down roots. When, in a gesture of camaraderie, a fellow soldier begins ticking off the names of the leading Jews in the rebel firmament, Abrams cuts him off. “That don’t mean they’re kin to me,” he says. “I run my own flag, case you were wonderin’.”

Abrams is fighting under the stars and bars, then, not because he believes in the cause but because, by enlisting, he avoids prosecution in New Orleans as an accomplice to murder. A self-interested semi-mercenary, he might have more in common with southern slaves, who later in the war, for a chance at freedom, joined ranks with passing Union forces, but that parallel doesn’t trouble Mr. Melman. The author suggests that we embrace war not for political reasons but for personal ones, that soldiers are driven to war by the same local forces that drive men to the altar and to the general store.

Tight-lipped and diffident, it can be hard to tell whether Abrams is meant to be an Odysseus, a Wandering Jew, or a bumbling Good Soldier Svejk. Like much recent historical fiction, “Landsman” yearns to be picaresque, but is more often capricious. With terrifying regularity, Abrams backs his way into situations that promise certain death, only to find increasingly improbable escapes. Is this war or just fanciful plotting?

The most unlikely development forms the very romantic core of the book. Early in his service, Abrams is handed a perfumed love letter, sent blindly by a New Orleans teenager, well-born, well-to-do, and eager to promise her heart to any Jewish Confederate. Returning her ardor in an exchange of heated letters, Abrams is a man transformed, “slightly stunned by the prospect of something nice in his life.” He tells his love that she is “the angel God has sent to one who is most in need.”

Like the story of war it punctuates, this epistolary romance is embroidered with the rococo affectation of period prose, and the novel is suffused with a familiar melodramatic longing — not of lover for lover, but author for era. Mr. Melman’s writing is strained by that longing, not enriched by it, as scene after scene is so lacquered with sentimentality it throws the actual drama into absurd relief. The result is a novel that wants to tell us things — about the Civil War, about the Jewish experience in America, about the way race and class are lived here — but “Landsman” is caged too tightly in its stylized sense of time and place to yield anything but a string of trite, homespun fables.

Mr. Wallace-Wells is a writer living in New York.