SOUTH CAROLINA'S St. Helena is a beautiful island, and Theodore Rosengarten knows its every lilt. Over a century ago there was a lord of that island, a man Rosengarten insists that we know, and when we do so, we find Thomas Chaplin a troubled, troubling and, importantly, an ordinary man. There is scarcely a thing about the cotton planter that is admirable, but like the tides that constantly stretch and then diminish his island, the story of the inexorable ebb of his life is remarkably affecting.

Thomas Chaplin, born in 1822 the great-great grandson of sea island planters, spent his earliest years at Tombee, the family place that still stands. When he was only 6 or 7, his father died and his mother, after marrying his clergyman-tutor, took him upcountry. Isabella Field Jenkins Chaplin Fields Baker, the mother, is much the most fascinating figure in the book; in the course of four marriages this sexy old tiger accumulated six plantations and 250 slaves and caught the eye of every lawyer who tried to outwit her. After a bit of schooling, Chaplin as a young man went back to Tombee, taking with him a child bride. If the island's slaves be excepted, Mary McDowell Chaplin led the saddest life of anyone in the story. Completely cut off from her own family, save her sister Sophy who ambiguously occupied one of Tombee's three bedrooms, Mary was wholly dependent on her husband and his connections. She had four children by the time she was 21 and three more by the time she died of a slow, painful illness at 29.

Thomas Chaplin, rich in comparison to 98 percent of his fellow Americans, was not, in sea island terms, a successful planter. He was forced to sell land, slaves, and worst of all, his boat in the 1840s. In 1847, he wrote, after recording the death of an infant daughter and Mary's attendant grief, "I am compelled to begin in the world again, not with forty but nine hands in the field. And a large family to support and educate . . . I know there are those who do not care to deal with me now, I am poor. But, by God's help, I may be worth something one of these future days, when I know how I will be again sought after and counted." It was only in the 1850s, when cotton prices soared, that he achieved a prosperity equal to the social status he sought to maintain among the island families and this prosperity was short-lived. The Chaplins -- Thomas had married Sophy after Mary's death in 1851 -- like the other planters on St. Helena, fled when the Union Navy seized Port Royal in 1861.

After the Civil War, Thomas and Sophy came back to the island where, ironically, they lived in an overseer's house and taught in a school for black children. Since Chaplin no longer maintained his journal, Rosengarten has tantalizingly few details, other than the tedious intricacies of the endless fight over his mother's estate, with which to recreate this period of the man's life. When the once-master of Tombee died, not on St. Helena but on the mainland, all but one of his children were dead and the survivor, mysteriously, had "despised and neglected" him. Just nine months before his death in 1890, "Chaplin was awarded 'redemption and restoration of title' " to Tombee, but he was never again to live there. ROSENGARTEN is not a writer afraid to get close to his sources, by far the most important of which is Chaplin's diary. This intimacy is announced by the fact that his volume contains not only Rosengarten's biographical study of Chaplin, but also Chaplin's spare journal with which to compare it. Rosengarten, while never an apologist for his unheroic hero -- he is achingly aware of Chaplin's insensitivity to the people who were his slaves -- has entered into the life of his subject so totally that his revelations about the man seem almost subjective. There are times, in fact, when the author is up so close that he cannot see where he has been. We are told on page 271 that, in the year following the Civil War, Chaplin was "forty-three years old, healthy and able"; but on page 34, we had learned that he "came back from the war an old man, shorn of his powers and fortune." Rosengarten seems to have done his writing far from his library; despite the rich literature on the history of slavery and emancipation, and his training in how to make use of it, one often feels that the writer nods to studies in the field only when scholarly friends remind him of books he ought to have read.

In a curious way, this deficiency is appropriate to the intimate telling of the story of a man who inhabited a very limited world. Rosengarten's view of the Civil War is drawn from snippets of data much like the disconnected information that a frightened, disoriented family, drawn ineptly into the war, would have had of an event that devastatingly and permanently altered their lives. As he demonstrated with his use of oral history in All God's Dangers, his brilliant portrait of the black sharecropper, Nate Shaw, Theodore Rosengarten is a writer who works from within. He does not try to make his study of a cotton planter fit into the arguments of more general histories of agriculture or slavery; instead, he goes to them in order to make large sense of seemingly small everyday occurrences in Chaplin's journal.

Tombee is not, strictly speaking, a biography; Chaplin's story is told not chronologically, but topically. It derives from the journal which ceases before the drama of the Civil War. If the study of the planter's life is, therefore, slightly static, it is no more immobile that Chaplin's life often seems to have been -- and what Rosengarten achieves is an immensely valuable study of how a planter planted, of his relationships with his family, his friends and his laborers. One of the striking concepts that emerges from the book is the sense in which the slaves were possessed not by an owner, but by an estate. Things were bad enough when dealing with the callous immediacy of a master like Chaplin; they were even worse when, as so often happened, the slaves found themselves to be simply the divisible property of quarrelsome heirs.

Nowhere in our literature do we have a portrait of a planter quite like this one. Neither William Faulkner nor Willie Lee Rose -- nor any of the other fine writers about the South who have looked at planters and at the sea islands -- have seen the creature quite as Rosengarten sees him. His is a study not of the dramatic collisions of human life, but of its banalities. With exquisite attention to the boredom of everyday existence at Tombee, he has made dull old Thomas Chaplin an unforgettable character. Rosengarten is a Chekhov to the Old South.

William S. McFeely, Richard B. Russell Professor of American History at the University of Georgia, is the author of "Yankee Stepfather: General 0.0. Howard and the Freedmen" and "Grant: A Biography."