SUMMERTIME By Maureen McCoy Poseidon. 300 pp. $15.95

"Walking After Midnight," Maureen McCoy's first novel, was the breezy story of Lottie Jay, a midwestern good old girl down on her luck and fighting back. The plot was simple enough -- men and booze and a hankering to write country music that leads the heroine to Nashville and the promise of a contract, but what was predictable about the story itself was compensated for by the author's language, as bright and snappy as Lottie Jay's polished fingernails.

In "Summertime," McCoy's new novel, the form of her tale is once again familiar: three women coming to terms with their pasts and their futures over the course of one hot Iowa summer, and once again it is the language, less frantic here but no less rich in energy and detail, that makes McCoy's simple story remarkable.

As the novel begins, Jessamine Morrow, 85, elopes with a man from her Des Moines retirement home. Alice, her widowed daughter-in-law, and Carla, her childless granddaughter, are startled and even threatened by the news. Since her father's death 15 months earlier, and throughout his 20-year illness, Carla has come to see the Morrow women as "being in possession of one overriding cultivation, the ability to live in the fragile condition of permanent inhalation: they lifted teacups to lips with alarming steadiness, meanwhile someone died." Her grandmother's bold step, Carla is certain, will somehow change all that. "She had released the tight, hard death-watching Morrowness still in effect, and set them all spinning."

For Alice Morrow the spinning begins on the very day of her mother-in-law's wedding, when she agrees to ride home with Mel, a widowed coworker. Until this summer, Alice has been the picture of emotional restraint. She has buried herself in her job at Craftique, purveyor of mail order crafts, filling her home with trinkets and hobby kits and salesman's samples. She has fed her squirrels and tended her yard and tied her hair into a tight bun, certain now, after her husband's long illness, after a loving marriage to a man who had returned from the South Pacific war unable to plan a life or imagine a future, that she is "done with the man-woman thing, truly deep, deep bone-weary done."

Carla, in her own state of permanent inhalation, has retreated with her predictable husband to the Iowa woods and an orderly life tied only to the seasons, but she, too, is set spinning when, the day after her grandmother's news arrives, she discovers she is pregnant. Panicked, she flees to Des Moines, to her mother and grandmother.

Throughout the hot, rainless weeks that follow, the events that mark these three women's lives -- a shopping spree, a retirement-home birthday party, a garage sale, an accident -- remain simple enough, and the gradual transformation of their spirits is easily foreseen: Alice slowly allows Mel to approach, even take her in his arms. Carla, in a marvelously strange and incongruously lurid scene, hears the voice of her child and accepts its life. Jessamine is threatened with another widowhood.

Yet it is not startling resolution or vivid insight that makes "Summertime" compelling. Rather it is the wealth of imagery and detail that McCoy offers the reader as the characters move through this summer of change and renewal. Whether she is describing the eclipsed suburban landscape of Des Moines -- a Sunday afternoon movie theater, a dying Kresge's, a family home taken over by bikers; the homely facts of a family's death watch ("Alice's ominous breakfast ritual: serving cereal from those little variety packs, milk poured directly into the foil-lined boxes ... Why make a futureless family endure the humiliation of economy-sized Cheerios?"); or the delicate, heartbreaking courtesies and manipulations of late love, McCoy is always a generous and exuberant narrator.

There are moments when it becomes too much, when the reader might wish to clear from the novel some of the bric-a-brac of metaphor and simile just as Carla clears her mother's pack-rat house of Craftique salvage, moments when the sheer abundance of language tends to blur the characters and temporarily disengage us from their lives. But these moments are few enough, and in the end "Summertime" rises above them. Wiser than "Walking After Midnight," more complex, certainly more ambitious, it is an impressive piece of work by a mature, intelligent, talented novelist who is just coming into full possession of her power.

The reviewer is the author of "A Bigamist's Daughter" and "That Night."