A Perfect Right to Break the Law : PARIS TROUT: <i> by Pete Dexter (Random House: $17.95; 304 pp.) </i>

Awell-to-do though reclusive businessman in a Deep South town shoots a 14-year-old black girl dead. The savage deed becomes a test of conscience for the town’s leading citizens, and of their courage or cowardice in confronting the social code they live by.

It sounds like something that could have been written by William Faulkner or Harper Lee 40 or 50 years ago. It takes place, in fact, just after World War II. The South, we know, has changed a lot since then.

Yet the fascination of Pete Dexter’s “Paris Trout” entirely surmounts any sense of thematic or literary harking-back. The violence seems minted yesterday in Cotton Point, Ga.; so does the evil in a berserk human spirit; so does the capacity of that evil to set all the complacent unsoundness of a society resonating, and then to jar it to bits.

The freshness is not in the theme, which is a perpetual one, anyway. It is in the intensity and subtlety of Dexter’s writing. His story moves us relentlessly and far too quickly to places we would rather not go, while making us marvel all the while at the dexterity and richness of the ride and leaving us unable to return.

In the person of Paris Trout, Dexter has created an authentic monster, unbelievable at first and then, bit by bit, compelling belief. He is a cold, solitary man who runs the town’s general store and has made a modest fortune loan-sharking to the black community and buying up property.

One day, accompanied by a henchman who was fired from the local police for brutality, he drives to the house of Henry Ray Boxer, who had bought an old car from him on time. Boxer returned it after a truck hit it, and Trout refused to pay up the insurance he had made him buy. Boxer, in turn, refused to make payments.

Boxer isn’t home. Trout pulls out a pistol and shoots Boxer’s mother, Mary McNutt, and Rosie Sayers, mortally wounding her. A day or two later, Trout is arrested and immediately released on bail.

The arrest is made with reluctance; the prosecution is conducted conscientiously, but with reluctance. Eventually, Trout is convicted and sentenced, again with reluctance, to one to three years in the workhouse. After three years’ delay, during which he writes his own appeals all the way to the U.S. Supreme Court, he surrenders to the sheriff who drives him, still reluctantly, to the penitentiary in the next county.

Trout has paid out $20,000 in bribes, however, and a crooked county judge orders his release. The next day he is walking around Cotton Point free, though facing the prospect of a jail term at the hands of an intractable U.S. government, to which Trout had never consented to file a tax return.

That, except for the ending, is the story. Or rather, the plot. The plot is the wiring. The story is the fearful current that Dexter sends through it.

Trout is a primal evil, all will and no humanity. We think “Snopes”--and he could be a demented Snopes kinsman. His dementia grows steadily, even after the initial slaughter, and yet it is built on a kind of principle.

It is Seagraves, Trout’s reasonable, even kindly defense lawyer, who first mentions the principle. “Paris Trout would refuse to see it,” Seagraves thinks when the police notify him apologetically that they will have to arrest his client. “That it was wrong to shoot a girl and a woman. There was a contract he’d made with himself a long time ago that overrode the law, and being the only interested party, he lived by it.”

To Trout, his action was perfectly justified. He had a contract; he had a right to enforce it. He is white and a somebody; Boxer is black, a nobody, and in default. The woman and the girl simply got in the way. They broke a rule; it was as if they’d jumped in front of a locomotive.

The fearful argument, the key to the story, is set out at the office of Towne, the prosecutor.

“If somebody got shot, they did it themselves,” Trout insists.

“Miss Mary McNutt in that case shot herself . . . let’s see, three times in the back?” Towne asks.

“Yessir,” Trout replies.

“You cannot enter a person’s house and shoot them dead,” the prosecutor says. “And that’s a dangerous rule to break too, sir. An eye for an eye.”

“Those ain’t the same kind of eyes and they ain’t the same kind of rules,” Trout says, smiling. “Those ain’t the real rules and you know it.”

Towne, who prosecutes successfully; Seagraves, who eventually abandons his client, and other influential figures in Cotton Point all abhor Trout’s killings and want to see him put away. But his argument speaks to their weakness. He is, in fact, the Frankenstein monster nurtured by their whole way of life.

It is a way of life that rests halfway between the laws on the books and the unwritten law of favors, arrangements and the exercise by the powerful of a kind of feudal right over the poor and the blacks.

The assumption, of course, is that this will be done within reasonable limits. Trout has broken the understanding by breaking the limits. “He has no brakes,” Seagraves says. He has codified the unwritten law and exposed the horror in it.

And so, until the book’s violent ending, when Trout goes totally out of control, nobody can take effective action against him. He is more violently determined, on principle, to stay out of jail than anyone is to put him in. Trout’s madness declares that society is ill; his declaration unmans it.

If “Paris Trout” is about a community hamstrung by its accommodations, it is also, at every moment, about the individuals caught in the accommodation. Dexter portrays them with marvelous sharpness; he knows his characters as well as God knows His, and this leaves them oddly free amid the design he has worked out for them.

There is Hanna, a talented teacher who, at 40, gave up her career to marry a man she was attracted to for his sheer animal force and independence. It was Trout, and it was the wrong kind of animal--cold-blooded. Hanna’s struggle to escape from him is a horrifying and beautifully told battle.

Her love affair with Seagraves gives Dexter an opportunity to write about sex as serious, healing magic. It saves Seagraves’ sanity, caught as he is between Trout’s grotesque parody of his own civic logic and the horror of the killings.

There is a young lawyer, son of a local minister, who comes back to town to fight Trout in a spirit of no compromise. He is right, and he is righteous; Dexter draws a fine balance between the human and inhuman aspects of being admirable.

The lawyer’s Northern wife is alien and isolated in the small town until she discovers a way to translate her sophisticated sexual liberation into the acceptable naughty sultriness of the traditional Southern Belle. There is a wonderfully comic party scene in which she puts on the guise of a latter-day Tallulah Bankhead.

There is other comedy; notably, a wonderfully protracted scene in which the sheriff transports a fully armed Trout to the penitentiary, only to find him descending from a bus in Cotton Point a while later. There is the dreamlike horror of the prologue, in which Trout’s rampage is told through the eyes of Rosie, his victim.

This extensive and beautifully written sequence is set in the black section of town. The whites, revealed in such sharp social and psychological detail later on, loom up here as blurred and ghostlike monsters. The monstrousness, even of the decent people, hangs over the entire book. Perhaps it is the reality that underlies the tragedy of manners. It is what merely unhinges Seagraves; it is one of the elements that make “Paris Trout” a masterpiece, complex and breath-taking.