FEW WRITERS have surveyed a century as magisterially as Dame Rebecca West did hers. She began publishing before World War I, wrote books on Henry James and D.H. Lawrence before they were canonical, covered the Nuremberg trials for The New Yorker, and has much to say about Watergate and the prime ministry of Margaret Thatcher. At 89 she recollected the century's dawning in 1900, a sketch of the world ruled by and accessible to England that year, which is positively coltish in its high spirits and obliquely angular insights.

When she died two years ago at the age of 90, she left an alp of manuscripts in various stages of completion: three novels, several short stories, a memoir of her parents, countless uncollected reviews and essays. This Real Night, one of the novels, is the first entry in what could be a posthumous book parade as long as Virginia Woolf's.

Fiction was not West's forte. With one exception her novels do not reach the heights of her four nonfiction masterpieces: Black Lamb and Grey Falcon, a monumental travel book (on Yugoslavia) that bursts the genre's seams; The Meaning of Treason, on British, American and Russian spies; A Train of Powder, reportorial essays on crime and trials; and The Court and the Castle, a literary look at the tension between religion and politics.

Among the mature novels, both The Judge and The Thinking Reed have their sparkling moments (West could hardly get through a page without framing a striking metaphor), but overall the material seems forced into shouldering the author's design. The Birds Fall Down has all the elements of greatness, but an extremely long, highly artifical conversation drains away its narrative energy. The common problem is West's failure to give her characters enough autonomy to dodge the pincers of her structuring mind. That conversation in The Birds Fall Down is disruptive because it reads like a lecture divvied up into Socratic parts.

THE NOTABLE exception to these strictures is The Fountain Overflows -- to which This Real Night is a sequel -- a loosely autobiographical treatment of an Edwardian childhood. Here West's gifts as a writer -- piercing insights into human behavior, formidable generalizing powers, a style that is exact, colorful, and fluent almost to the point of flood stage -- combine with imagination and carefully controlled nostalgia to produce a novel reminiscent of late Dickens. It has a poltergeist, a murder, a trial, blackmail, perhaps the most convincing portrayal of musicians in all of fiction, and at its center a mesmerizing family.

Piers Aubrey, the father, is a brilliant writer who sells his talent short by playing the stock market, always counterproductively. Constantly in debt, he is reduced to editing a suburban newspaper to support his family. His wife, Clare, was a virtuoso pianist who scrapped her career to have children and must now stretch the family's meager means to ingenious lengths. Cordelia, the eldest child, is an egotistical violinist manqu,e whose red-curled beauty tends to hide her tin ear. Rose (the narrator) and Mary, twins, are budding pianists driven to distraction by Cordelia's preening ineptitude. Richard Quin, the baby of the family and everyone's golden lad, has an unfailing knack for familial diplomacy.

West develops this group into as vivid a set of dramatis personae as fiction can muster -- and I haven't even mentioned Miss Beevor, Cordelia's dowdy, love-stricken teacher, or Cockney Aunt Lily. Even when they say things that are pure Rebecca West (Piers Aubrey: "Thought that is worth calling thought has no mercy on itself, that is the dreadful proof of its quality."), so much individuality has been poured into them that they still sound like themselves.

This Real Night does not measure up to its "prequel." For one thing it is not really finished: it may stop, in the publisher's phrase, "at a dramatic point," but not a final one. West must have run into repeated difficulties in continuing the story. She had written the early chapters of this book by the time The Fountain Overflows came out in 1956, but about 1970 she informed an American scholar that she'd abandoned the second Aubrey book. Now it appears that she not only intended to finish it after all but planned a trilogy. Several more chapters exist, along with an eight-page synopsis of the whole, and all of this may eventually be published.

The totality was to be called Cousin Rosamund: A Saga of the Century, which brings up a second weakness in the sequel. Two of the most watchable characters from the first book are all but absent. Though on the scene in everyone's memory, Piers is literally gone -- he absconded at the end of The Fountain Overflows because he couldn't bear what he was doing to his family -- and Cordelia, having given up the violin, is a vixen turned pussycat. The focus shifts to cousin Rosamund and Richard Quin, but she is a stolid nursing student and he gets less interesting as he grows up.

Even so, This Real Night contains many dramatic episodes and remarkable passages. For example, there is this description lavished on a cameo character: "His eyes were black fire among his finely incised wrinkles, the bones under his yellowing ivory flesh might have been put in by a fan-maker." And there is Rose's anticipation of her mother's death: "Existence was about to split into two, and Mamma was to be on one side of an abyss and the rest of us on the other."

Simultaneously with Viking's publication of this book in hardback, its Penguin affiliate is bringing out The Fountain Overflows in paperback. Anticlimactic though This Real Night may be, between them the pair comprise more sterling prose and vitalized characters than most completed sagas. By all means read the first book, and here's betting you won't be able to stop there.