By Owen Parry

Avon. 338 pp. $23

Reviewed by Ken Ringle

"A sentry with troubled bowels discovered the body. A shock it must have been for the boy. He fired off his rifle and the Good Lord knows what else, then ran up through the mud and fog to his camp. I do not fault the lad, you understand. A . . . boy new to service, touched with sickness and the autumn chill upon him, such a one might be forgiven a wallop of fear when he tumbles over a dead officer in the pursuit of a winkle of privacy."

So begins Faded Coat of Blue, Owen Parry's immensely rewarding novel of Civil War Washington. At first glance it promises to be just another period whodunit -- a murder mystery dressed up with the academically trendy mutton-chop whiskers of 19th-century social history. But Parry has aimed far higher than that, and before he's through he's led us through a genuine novel of ideas: a provocative examination of moral values and history as irresistibly readable as George MacDonald Fraser's "Flashman" books but as serious as they are flip.

The superficial vehicle for his story is the search for the killer of Anthony Fowler, a physically beautiful, socially prominent young abolitionist found shot to death mysteriously in a Union camp south of the Potomac in the first autumn of the Civil War. The real story of the book, however, is that of its narrator, a diminutive Welsh-born Union soldier named Abel Jones. Jones has immigrated to America after service with Queen Victoria's army in the Indian Mutiny, and his moral turmoil over that ghastly bloodbath and its equally ghastly reprisals has led him to a lonely search for duty worthy of the liberating democratic promise of his adopted homeland.

He's a wonderfully improbable protagonist, a consummate professional soldier now reduced to supply clerk after being crippled by a runaway wagon while trying to rally his fleeing troops during the Union debacle at Bull Run. He's chosen by Gen. George McClellan, leader of the Union Army, to solve Fowler's murder before abolitionist zealots can make the charismatic young man a martyr and turn the war into an anti-slavery crusade that would make negotiated restoration of the Union impossible.

But as Jones plies his Victorian earnestness through the thorny political thickets of Washington, he finds himself decoyed and manipulated at every turn. He loathes slavery but finds abolitionists self-righteous, deceitful and hypocritical. He lionizes McClellan but finds himself betrayed by the little general's deviousness. He hates war profiteering but discovers some profiteers more honest and humane than many of his own leaders.

His quest becomes a kind of pilgrim's progress: As impressive as Jones's compelling character and voice is Parry's vivid recreation of the nation's capital in its war-torn adolescence, teeming simultaneously with aromatic whorehouses and horse-carriage vanity; a snake pit of backstreet violence, disease and wretchedness in the shadow of a Washington Monument as ambitious and unfinished as the city it will one day symbolize.

Jones's Washington swarms with immigrants, many of them fugitives from the European revolutions of 1848, and many more of them Irish starved into American citizenship by the Great Potato Famine. Which is morally worse, Jones wonders: the institutional cruelty and injustice of slavery in the South or the social and economic chattelhood in which the dispossessed of Europe are frozen by brutal indifference in the North? Can the United States ever hope to solve one problem without solving the other?

It will be the bloodshed of those new Americans, Parry reminds us, that ultimately will save the Union and free the slaves. And the author unashamedly tips his hand with his dedication "to the Welsh, Scots and Irish who built America while the English weren't looking."

So successful is Parry with his characters and verisimilitude that at times his plot is almost a distraction. Toward the end of the book it threatens to trip over itself and the author forces a solution a bit with a lanky, bearded deus ex machina in a stovepipe hat. But by then we don't care. He has given us something far more enduring than mere page-turning entertainment: He's immersed us in that other world and taught us its lessons.

He never stoops, as so many authors of historical fiction do, to anachronism of character, by making Jones the sort of stock, world-weary cynic who populates novels of the 20th century. Instead, he risks propelling his book via his punished immigrant narrator's touching, transcendent faith in the promise of America. In the hands of a less skilled, less purposeful writer, that could easily succumb to simple-mindedness or sentimentality. In Parry's hands it never does -- for Jones's earnest voice is the Victorian faith in a better tomorrow as the reward of godly courage, self-discipline and industry. And that becomes the ultimate signature of Parry's mature and finely wrought tale.

Ken Ringle is a writer and critic for The Post's Style section.