Star-Crossed in the South : SLOW POISON <i> By Sheila Bosworth</i> , <i> (Alfred A. Knopf: $21; 322 pp.)</i>

Springing from the late Walker Percy’s hometown of Covington, La., novelist Sheila Bosworth appears ready to take up the mantle of the great writer himself, substituting for his metaphysics the plain-talking verities that turn commonplace fiction into a work of art. In “Slow Poison,” her second novel, Bosworth does a splendid job of irradiating the murky truths of an old Southern family in a cautionary tale of love, hate, pathos and redemption that would make an old master like Percy pretty proud.

Rory Cade, now in her 40s and a successful Hollywood writer, meets an old flame, the infamous political journalist J. B. Killelea, for drinks at New York’s Plaza Hotel. The subject of the conversation is a letter from home announcing an impending death in the Cade family. Soon the two are airplane-bound for southern Louisiana. In the dimness of the flight through a stormy evening, Rory recounts the saga of the Cades, and the reader sinks into the tale of this star-crossed family just as neatly as slipping into the waters of a warm old swimming hole.

New Orleans has to be the most exotic city in America, and Bosworth writes about it as well as, if not better than, anyone else. What the novelist Anne Rice does for New Orleans ghosts Bosworth does for the real thing--the old Southern society hovering between decadence and respectability, hanging by a thread to the latter while clawing desperately and unsuccessfully against the former.

But the travails of “Slow Poison’s” characters aren’t only Southern. They’re the same as for so many modern American families: a spiritual deracination and an inability to fully grasp their fate. They don’t know what’s going on--let alone what to do about it--but they try. Bosworth’s people are trying so hard to sort out the anguish and puzzlements in their lives that even the author intimates they are crazy when, in fact, they are just as sane--most of them at least--as, say, Sigmund Freud.

In her first novel, “Almost Innocent,” Bosworth explored the world of Rory’s mother’s side of the family. Here the tale is of her father, Eamon Cade, a physician, scion of the Cades of Covington, La., an exclusive enclave north of New Orleans. But Eamon Cade is no dandified Southern scion. As his story is revealed, we learn that he grew up in penury, scrambling for whatever he got, until he finally married rich and started to drink himself to death.

The book takes its name from Turgenev’s line about women’s love being a “slow poison,” but the title might as easily apply to another major theme of the story: the inevitable toll that whiskey and tobacco take on the soul and body--since so many of the major characters in the book stay plastered, surrounded by a blue cloud of cigarette smoke to escape their troubles.

Rory recounts how she and the other two Cade sisters grew up during the 1950s, reared after their mother’s death by their father and a maiden aunt, until the following decade, when the 1960s blew it all apart. Older sister Jane Ann marries a boy fated to go to Vietnam as a Navy pilot; younger sister Arabella becomes an introspective artist; Rory herself gets entangled with J. B. Killelea (now partner in her airplane ride), a darkly amusing, two-fisted, boozing mirror image of her own father, Eamon. The main twist in the story, which will not be revealed here, is how Johnny Killelea manages to marry both of Rory’s sisters.

What can be told, however, is how the author combines an intimate and understated wit with an outrageous sense of the absurd to illustrate a family about to come apart at the seams. We learn of silver punch bowls and fine old lace, of waxed-wood floors and high-ceilinged homes and fraternity parties at Tulane and the family car, an ancient Bentley. And, as much a part of the family as everyone else, there is a trio of loyal black servants whose running observations on the pseudo-lunatic goings-on in the Cade household provide grandly insightful comic relief.

If there is a quibble at all with this book, it is that some sort of family tree would have been nice up front, to help the reader sort out the various relationships that evolve in the first 50 or 100 pages. But after that, the ship sails smoothly toward its final destination with the writer steering with a firm hand and the Cades holding on--or trying to--amid a world of crumbling values and other things they do not really understand.