CLOVER ADAMS, who presided over the most rarefied Washington dinner table of her day, was so uppity about the company she kept that she refused to speak to the secretary of state, pronounced the chief justice "unutterably vulgar," and barely condescended to dine at the White House. Alas, Clover has remained one of Washington's great mysteries, and her pungent letters about life here in the Gilded Age are an inside secret. Clover's husband, Henry Adams, historian, novelist and descendant of presidents, all but erased the traces of his wife's existence when she died in 1885 at the age of 42. Read his books and you would not know that Clover Adams lived at all. Except for Clover's published letters (out of print and hard to come by) and the Saint-Gaudens statue at her unmarked grave (hard to find in Rock Creek Cemetery), all that survive are questions: Why did she kill herself at her home on H Street when, as one friend said, she had "all she wanted, all this world could give except perhaps children?" Why did Henry Adams fail to mention her name in The Education of Henry Adams -- in fact, cut the entire 13 years of their marriage from his autobiography -- the very years, he later wrote a friend, "I had everything I wanted most on earth?" What kind of marriage was there anyway between these two shy, self-conscious, Cerebral Boston Brahmins?

Probing these secrets is the central mission of Otto Friedrich's Clover . If his biography does not produce all the answers, it thoroughly explores the questions. He turns up enough evidence in family attics and archives to rescue Clover Adams from oblivion and place her firmly back where she belongs -- in Boston at the time of the Civil War and Washington from the administration of Rutherford B. Hayes (1877) to Grover Cleveland's first inaugural (1885).

Clover was born Marian Hooper in Boston in 1848. Although not as eminent as the Adamses, her family was venerable and respected. The tragedy of her childhood was her mother's death from tuberculosis when Clover was five. Thereafter she was markedly devoted to her father, William Hopper, "one of the pleasantest fellows," according to his friend and fellow physician, Oliver Wendell Holmes.

By the time they discovered each other in Cambridge in the early 1870s, Henry Adams was the radical of the Harvard history department, in his mid-thirties, balding, frail, "a timidly arrogant genius." Clover Hooper kept house for her father, was said by her friend, Henry James, to possess "intellectual grace," and seemed on her way to spinsterhood.

Henry Adams described his fiancee to a friend in typically ironic words: "She is certainly not handsome; nor would she be called quite plain . . . She knows her own mind uncommonly well . . . She reads German -- also Latin -- also, I fear, a little Greek . . . She talks garrulously, but on the whole pretty sensibly. She is very open to instruction. We shall improve her. She dresses badly. She has decided humor and will appriciate our wit."

The wonder is, as Friedrich says, that these two "prisoners of their own refinement . . . equally crustacean . . . each swimming alone in frozen oceans, should have managed to find each other, and recognize each other for what they were, and love each other." And love, apparently they did. At least it seems so from the letters of Henry's older brother, Charles Francis, describing them as "the most married couple I have seen . . . sitting together and she holding his hand . . . my much married brother and his dotting spouse."

It is in the series of Sunday letters to her father -- begun on her wedding trip in 1872, continued at home and abroad for the 13 years of their marriage -- that Clover really comes alive. She is observant, funny, caustic, gossipy and critical of nearly everyone she meets. Even in England where there were invited everywhere, she found much to scorn. Lady Salisbury, she once wrote, "has the manners of a discouraged cook." Robert Browning "is not attractive"; all English parties are "stiff and dull." But her descriptions of Washington -- where they moved in 1877 -- form a priceless record of "the only place in America," as Henry Adams put it, "where society amuses me, or where life offers variety . . . although our politics just now are very deep in the mud . . . still it is fun to see [our politicians] wriggle."

While Henry settled into writing history, Clover gathered around her tea table only the most impeccable -- high-minded reformers, foreign ambassadors, a few unsullied senators. No whiff of scandal, no taint of corruption, no waft of the vulgar rabble made it past her door. The Adamses refused to "bow" to Secretary of State Blaine (more than a whiff of scandal clung to him); Clover fretted lest visiting Oscar Wilde might come to call ("I must keep out thieves and moodles or else take down my sign and go West," she wrote.)

Clover's letters tell of the delightful ease in Washington in the 1880s, which the visiting Henry James described as "indefinably ridiculous and yet eminently agreeable . . . the sky is blue, the sun is warm, the women are charming, and at dinners the talk is always general."

Nearly every fine morning, Clover and Henry Adams rode their horses out along the river or across Chain Bridge or out to Soldiers Home. (Their nieces remembered them in Massachusetts in the summers: "two figures on horseback. . . . An impression of oneness of life and mind, of perfect companionship.") "This part of life." Henry confided to a friend, " -- from forty to fifty -- would be all I want." If he was contented, Clover, perhaps, was not. Through her tart and saucy letters to her father runs a thin but unmistakable thread of melancholy -- like camouflaged homesickness in a child's letters home.

In 1882 Clover took up photography. In 1884 Henry Adams and John Hay commissioned Henry Hobson Richardson, their friend the architect, to design adjoining houses for them across LaFayette Square from the White House. When the houses were half-built, in April 1885, Dr. Hooper died. After eight months of deep depression ("We broke down," Henry Adams wrote a friend), Clover Adams killed herself by drinking potassium cyanide, a darkroom chemical.

Friedrich offers many -- to many -- theories to explain her suicide. The most obvious is probably the best: her father's death triggered emotions, buried since the loss of her mother in early childhood, that overwhelmed her. Clover's sister and her brother later chose violent, punishing forms of self-destruction (one jumped under the wheels of a train, the other out a third floor Boston window). What this reveals about the impact of their mother's loss, or about the suggestibility of Clover's suicide, or about family instability we will probably never know.

"In my whole life," Henry Adams wrote Elizabeth Cameron years later, "I met only one woman whom I wanted to marry, and I married her." At Clover's death, he wrote, "Life could have no other experience so crushing." His reaction to that blow -- burying it in privacy and silence -- is what makes Clover Adams such a tantalizing mystery, a mystery intricately analyzed and only partly dispelled by this book.