Nothing Recedes Like Excess : A WOMAN RUN MAD <i> by John L’Heureux (Viking: $17.95; 272 pp.) </i>

If John L’Heureux had wanted an epigraph for his comic horror story, “A Woman Run Mad,” he could have used Goya’s ambiguous inscription, in one of its possible translations: “The dream of reason brings forth monsters.”

The book’s four main characters represent in different ways the rational flower of our contemporary urbanity and the canker that eats it. They live in the gracious part of Boston, and they are more or less talented or charming or funny. The worst one is selfish and self-centered, but in a comfortably recognizable way. By the end of the book, they have fallen into madness and monstrosity.

In Sarah, a handsome and cultivated Brahmin, the madness is visible from the start, though misted by a vulnerable allure. Quinn, who taught English at Williams College and is now trying to write a novel, encounters her shoplifting a purse at the Back Bay branch of Bonwit Teller.

He is intrigued; and anyway, his writing is going badly. He follows her to her Beacon Hill apartment, only to be accosted on the doorstep by a young man who makes a crude sexual overture.

We learn at once--Quinn learns more slowly--that Angelo, the young man, is the brother-in-law of Sarah’s brother Porter, and his lover as well. Uncontainably promiscuous, he spends his non-cruising hours reading Kierkegaard and Camus.

He has also been appointed to keep an eye on Sarah, who some years earlier had killed and mutilated a sexually sadistic lover and had escaped jail by a judgment of temporary insanity. When, at the end of the book, we learn the details of Sarah’s mistreatment and her reprisal, they are so terrible as to blur the lines between the two and arouse a kind of desolate sympathy for her.

The above may begin to tell us what L’Heureux, a moralist of untrammeled imagination, is doing. But it takes us a long way from how he is doing it.

The horror in “A Woman Run Mad” is both serious and extreme. But we get to it gradually, by way of premonitions in which we have no real trust, in the course of a book that is blithe, witty and so coolly laid back as to constantly tell us that nothing really awful can be happening.

It is like dining in the most sophisticated of French restaurants, imagining we hear an occasional whisper of “poison” from the direction of the kitchen and reassuring ourselves that quite clearly we must have heard “poisson.” And ending dead.

The blitheness begins with Quinn and his wife, Claire. She has prevailed over handicaps--orphanhood, poverty and a tendency to get fat--to become a brilliant Latinist and win a tenured position at Williams. Quinn, on the other hand, is shallow and self-absorbed. When he fails to receive tenure, he and Claire work out an arrangement under which he will spend the summer writing in a small Boston apartment and she will commute weekends.

There is an angry passion in Claire, but it is concealed--from herself among others--by a need to put aside her former ordeals and find gentleness and repose. She is actively winsome; she says “Quid?” for “What?”, and when she succumbs to a cinnamon roll, she calls herself “Porcus ultimus.” She clings to Quinn and is confident that he shares her commitment to marital coziness. For a while, we will get rather fed up with Claire.

Quinn does. Sarah’s shoplifting seems exotic to him when he first spots her. So does the languorous and kinky sex she introduces him to when they finally get together. A touch of perversity is appropriate to the contemporary urbane. Even Angelo’s cruising doesn’t make him a monster, though it does get him savagely beaten up; he is genuinely kind to Sarah and loves to talk about ideas.

Quinn settles in to his summer fling. In his calculated way, he begins to write his novel about it. It is not long before Claire finds out what is going on; but she figures that she can wait things out. Quinn, on the other hand, begins to believe he would be better off ditching Claire and marrying Sarah, who longs to escape from her madness and her memories into a normal life.

Normality--as our time understands the word--and monstrosity are L’Heureux’s poles, and he joins them with extraordinary dexterity. Sarah and Angelo, despite a sweetness that finally attaches us to them, are the monsters, seemingly. Quinn, despite his unlikableness, and Claire, despite her excessive striving, are the normal ones, seemingly.

The ending is not to be revealed, other than to say that it is bloody and grotesque and that normality and monstrosity become utterly indistinguishable.

But it is in his style as much as in his plot that the author manages to connect his opposites. “A Woman Run Mad” is, for much of the time, witty and almost lighthearted. L’Heureux treats his characters somewhat in the manner of Iris Murdoch; even in their most matter-of-fact moments, we feel a horror closing in on them without knowing where it comes from. Conversely, representing large and terrible things, they are chatty and crotchety and sometimes very funny indeed.

There is the comedy of Quinn trying to turn his erotic sessions with Sarah into fiction. His notes read like a plumber’s manual. “Wasn’t writing about sex a lot like trying to re-create the first time anybody ate a baloney sandwich?” he asks himself.

L’Heureux, in a sentence, can convey enormous pain. Quinn has told Claire he will leave her. She walks out, swivels and tries to come back in; he holds the door shut against her. “They stood there, pressing wildly against one another, the heavy door between them,” L’Heureux writes in a stunning reverse image.

The author is not always in full command of his odd and original novel. It bogs down in a series of internal monologues, particularly Claire’s and Angelo’s.

Having Claire discover a pistol in Angelo’s bedside drawer early on, and introducing a peculiar little boy who spends his day sitting on the staircase and watching what is going on, may recall Chekhov’s caution: Show us a pistol in the first act and we know it will go off in the last. Show us a watch bird at the start, we might add, and we know he will see something before the end.

“A Woman Run Mad” is quirky and unbalanced. Its excesses at the end hardly seem excessive, and that is the author’s remarkable achievement. It is accomplished at the price of a large distancing.

It is hard to feel close to this talented book, which is clever most of the time and wise at least some of the time. It may be hard to love it. Perhaps it is not hard to dislike it. It is easy, in any case, to admire it and its author extravagantly.