By Sally Beauman

Bantam. 786 pp. $19.95

THE GREAT COUNTRY houses of England have a peculiar fascination for Americans. Winterscombe, which is the primary setting for Dark Angel, is no exception. Here again are the familiar terraces and gardens, the stables, hothouses and tennis courts, the vast lawns, the river and the woods. Here again are the long corridors and enormous rooms, the attending servants, the house parties and the hunt parties -- hunting animals is the chief male pastime -- in an ambience that, in spite of its familiarity, is still alluring.

The story opens in the present, as Victoria Cavendish -- a proper name for a girl born and reared at Winterscombe -- sets out on a search for her godmother, Constance Shawcross, the "dark angel" of the title. These two women are both pre-eminent interior decorators for the sophisticated super-rich in New York, and have been partners, but an old tragedy at Winterscombe, never resolved, has brought about a bitter separation. Now after many years, Victoria is driven to discover the truth of that tragedy, and she believes that Constance, secretive and strange, may know what it is.

In the month of April, in the year 1910, on the night when Halley's Comet raced splendidly across the sky, Eddie Shawcross, the father of Constance, was found dead in the woods near the house. He was a houseguest and secret lover of the lady of the house. The manner of his death was particularly frightful: Someone, for some unknown reason, had set out a "man trap," a human-size device exactly like the bone-crushing, iron-toothed, agonizing traps that are used to snare animals. It had been discarded long before and was of course an illegal instrument.

Who put it there? And who, in the dark of midnight, lured Eddie Shawcross toward torture and death?

At the time, after fruitless investigations, it was concluded that he had died by accident. Yet those who were present then had reason to think otherwise, for there were few in that great mansion that night who might not have had some reason to hate him.

Old mysteries fade, however, and two world wars have blotted out many memories. It is only a combination of two circumstances that awakens in Victoria an intense desire to know: the first is her nostalgic return to Winterscombe which, like many grand country places, has become a white elephant and is now in the hands of the real estate agents; the second is her receipt from Constance, with a covering letter, of Constance's own journals:

"My dearest Victoria,

"Are you sitting comfortably? Good. Then I shall tell you a story . . . about Winterscombe, your family, your parents and me. It is also about a murder -- is it a murder? -- so pay attention as you read."

From this point, the story continues in repeated flashbacks; very many characters are involved -- from Victoria's grandparents, Denton Cavendish and Gwen, his American wife who loved Eddie Shawcross, to Victoria's mother Jane and her father Acland, who might well have been the murderer. Yet in spite of this complexity, all these people are clearly and skillfully presented in their variety and with keen comprehension of the conflicts, including sometimes madness, that lie behind every human facade.

Beauman's research into the social scene as manners and mores evolve from the early 1900s through the 1980s is admirable. She describes, for example, the nuances of class distinction: the begrudging mixture of hostility and respect with which aristocratic England looks upon Montague Stern, the Jewish financier and husband of Constance; the passions of Acland, the son, and Jenna, the servant, passions that can never end in marriage between them, which Jenna understands and Acland, age 16, possibly does not. There is here a keen sensitivity to vivid and authentic detail, from the cut and fabric of a child's dress to the battlefield hospitals of the First World War, where Victoria's mother goes to search for the missing Acland.

To this reviewer's taste, however, an eye for detail can sometimes be too keen and exact. Some of the vivid details of the many -- too many -- sexual encounters that occur throughout the story might have been spared, in particular, a stomach-turning description of a father having sex with his 5-year-old daughter. At the same time, this reviewer is also quite aware that for some readers that kind of ultra-realism will enhance the excitement of the book, and not mar it.

Many other readers will appreciate for its own sake the author's command of language. She uses English, that good, rich, flexible tongue, with expert ease, which is surely refreshing in these days when English is so often lamentably mangled on the printed page. Her descriptions of people, places and weather are evocative; her dialogue is knowing, accurate and true to each character. She delves successfully into the mind of each character, especially into the mind of Constance, the baffling child grown into a woman dazzling, provocative, loving and cruel.

The novel is lengthy, but suspense never wanes while it moves toward a conclusion as shocking and unexpected as the denoument of Du Maurier's Rebecca. To the many readers who admired Beauman's previous novel, Destiny, this book will give great and equal pleasure.

Belva Plain's latest novel is the forthcoming "Harvest."