By Shelby Hearon

Atheneum. 306 pp. $18.95

The family is always there first in Shelby Hearon's novels. But it's not a nice, neat nuclear family. There's usually some male who's way out of line, out in his own orbit, a man who has thrown the rest of the group into a spin. Whether through promiscuity or spinelessness, he has abandoned the family and left the women behind. So the female kin hang on to each other, but God knows why; no one would ever mistake them for a support group. Mothers forsake mothering for careers. Sisters resent each other. Daughters hate their mothers. The fat female cousin, the family embarrassment, is shipped out to live in the old decrepit country place. But at the same time, none of these women let go. They get together to cook, clean or mourn, all in the name of family. These women don't really trust each other, but the rest of the world is so full of deceit that even dubiously loyal kinfolk look relatively better.

"Five Hundred Scorpions" is Hearon's 10th novel. The previous three hit in rapid fire, one a year: "Afternoon of a Faun" in 1983; "Group Therapy" in 1984; and "A Small Town" in 1985. These were wonderful novels about small towns and tough women, books that played with character and voice and dealt in a natural and nontortured way with changes in women's lives. They were novels that were driven by emotion first, then only secondarily by the need to deal with women's issues. Whatever concern bothered the vanguard of the women's movement, Hearon showed how it would play in Peoria. In her small towns, an offense against women didn't inspire strident dialogue. More than likely, the women sat down at the kitchen table and figured out a way to run away from it.

"Five Hundred Scorpions" is more adventurous than the three novels that immediately preceded it. Paul and Peg Sinclair have been married more than 20 years and are living in Charlottesville, Va., when Paul, 48, suddenly decides to split. It's a quintessential midlife crisis: the lawyer ups and leaves his wife and two sons and heads for Mexico. He hops the first plane for Tepoztla'n to work with an anthropological team headed by two women. But it's not skirts he's chasing; his is an intellectual pursuit. For a while.

It's the classic situation. Helena, the head anthropologist, is a stunning blond, committed to her work, but icy, enigmatic and not completely trustworthy. And Peg, the wife Paul leaves behind, is a woman who dabbles, who takes too many adult education courses and who has no commitment, no full-time occupation other than driving her oldest son to his tennis matches. It's a nice way for Hearon to get at this unfortunate war waged between women who work and women who don't, in which both sides wind up hating each other -- an unfortunate byproduct of gains made in the name of women's liberation.

To really add fuel to the flames, Helena and her female colleague Jean are on a particularly feminist mission. They have come to study the town of Tepoztla'n because although the Mexican village has been swarming for decades with anthropologists curious about this picturesque patriarchy, the research has always been carried out by men. Helena and Jean, ace social scientists, know things are skewed. Their mission is to prove that, contrary to previous research findings, the average man in Tepoztla'n is being led around by the nose. By women.

It's Mexico that really throws this book off the track. The small American town -- that life-support system so vital to Hearon's previous characters -- doesn't translate. Of course, in Paul's case, it's not supposed to. Paul, transplanted from Charlottesville, is always out of step and out of breath; the air's too thin or something. But the whole anthropological plot line is so forced that all of the characters involved, even the Mexicans, seem strained and artificial, painful creations of somebody's research but not of somebody's imagination. Hearon's strengths -- characterizations and dialogue -- stayed behind in Charlottesville with Paul's business suit. The Mexican village is supposed to be warm and friendly, like any small town, but it's also supposed to be mysterious. Paul, as part of the research project, is asked to try to uncover some village rituals, male secret-society-type stuff. But his mission is forced and flat; he's an American lawyer dressed in vacation clothes, wandering through Borges land.

As for the battle between women, nobody really wins, especially women readers. The female anthropologists are made to look like profession-hungry harpies, using men in the name of social science. And it's not easy to like the forsaken wife. Her name is Peg but it ought to be Patsy. She does only a brief stint as the proud vindictive wife before she cops out completely. We've all heard men say, "My wife doesn't understand me." Unfortunately, Peg is the kind of woman who gives legitimacy to that lament.

It is easy to understand why a talented and prolific writer like Hearon would want to push her horizons, especially on her 10th novel. Like many of her characters, she's ready to travel beyond her small towns. Next trip, maybe next year, she'll pack more emotional baggage.

The reviewer is a senior editor of The Washington Post Magazine.