SANDMOUTH By Ronald Frame Alfred A. Knopf. 476 pp. $19.95

This is a book that begins and ends with a body. Yet it is not a detective story or even a novel of suspense, at least not in the accepted sense. Still, the puzzles here are myriad and the clues equally numerous, while the truth is simply this: Everyone has something to hide.

Always an intriguing idea, if not a particularly original one, this notion is stretched by Ronald Frame to cover a fair sampling of the populace of Sandmouth, an English seaside town. The time of year is early spring, the period, the mid-'50s, and the action takes place over the course of one eventful day.

From the first character we briefly meet, Alma Stockton, the local telephone operator (whose careful accent is false and who sometimes can't resist listening in on calls), to the last, nobody is exactly who or what he or she seems to be. Petty concealments are the rule, although there are a few folk in Sandmouth who have the kind of secrets that wreck lives, if not neighborhoods.

For example, the tormented husband who daydreams of small boys and attempts to keep his wife from the realization that he loathes the sight of her. Or Nanny Filbert, a dissolute child-minder straight out of the lowest reaches of Dickens, whose idea of an afternoon's work is to drug her young charge unconscious.

Then, too, there are the citizens who've reinvented themselves for the purposes of Sandmouth: Mavis Clark, born Irene Sweeney, who's exchanged her sordid London origins for an imagined gentility, or the Symington-Berrys, who run the local prep school and aren't quite as refined as they've trained themselves to appear.

And there are the people who have, for either practical or pathological reasons, invented someone else! Into this category falls Mr. Selwyn, an antiques dealer whose so-called employer, Miss Arbuthnot, doesn't actually exist; rather, she is "a commercially justifiable ploy" to keep him off the hook with the public whenever he needs to cite a higher authority.

A sadder case, though, is Ruth Aldred, the vicar's daughter. Unmarried and still living in her father's house while doing the requisite good works in the parish, she would seem to hold very little interest. But, in fact, since childhood her docile exterior has masked a firmly entrenched second personality -- that of her twin sister Constance, who died at birth along with their mother.

"She recognized that it was the merest chance that had made her 'Ruth' and not 'Constance.' She might have been Constance . . . Constance had had as much right to the privilege of 'life' as she did . . . Thus Ruth Aldred was deeper and more complicated than the folk of Sandmouth -- good or not -- suspected."

Whether by reason of adultery, illegitimacy, phony war records, shoplifting, whatever -- the author is relentless in his cataloguing of human duplicity -- throughout Sandmouth, skeletons are poised, waiting to fall out of closets.

Their rattles, then, are what form the plot, such as it is.

With these and so many other characters to keep track of, each taking turns at center stage, and with so many secrets unfolding, a reader can't be blamed for feeling a bit dizzy. But more troublesome is Frame's dogged schematism.

Nor is Frame the least bit deft about what he's up to. By making Tilly Moscombe, a 16-year-old half-wit who wanders in and out of every significant scene, the repository of Sandmouth's secrets and the scapegoat for all of the frustrations engendered by so much guilt, he settles for what amounts to a cheap effect. From the very beginning, poor Tilly is marked for tragedy, and Frame's methods of foreshadowing her fate are about as subtle as a total eclipse on a sunny day.

Mrs. Dick, the doctor's wife, is really the only figure in the novel who spends any time musing on the Big Picture. Introspective and cynical, her secret is that she's not the placid helpmate and mother she might seem to be. "Sometimes {she} was privy to very treacherous thoughts which seemed to strike at the root base of those assumptions everyone lived by." But there's too little Mrs. Dick in "Sandmouth" and too much of the ultimately tiresome submerged selves of the Sandmouth inhabitants.

Frame has undeniable talent as an observer of human behavior. And one can't but be amused by his occasional forays into slapstick: say, the messy climax of the school fete or the ludicrously grim fate of a greedy deathbed hanger-on. And certain of his portraits are memorable: the has-been and never-was actress Adele Adaire; or the novelist Miss Vane; or the not-quite indomitable Mrs. Symington-Berry.

"Sandmouth" is a flawed book, but one that remains fascinating in its ambition. Intended also as a picture of the changing mores of postwar Britain, it does create a recognizable world in a distinct era. Mostly, though, one regrets that Frame didn't trust that his readers would be able to follow him through this landscape on their own, without the cement footprints he leaves for them to step in.

The reviewer is the author of "Momilies: As My Mother Used to Say" and "More Momilies."