A NOVEL FROM Doris Grumbach is an event, and Chamber Music does not disappoint. It is a book of originality and distinction. The change of key in the last movement, while it may seem self-defeating to some, will be central to the discussion that the novel is sure to provoke. Chamber Music is presented as the memoirs of an old woman born in the 1870s; Grumbach has felt it necessary to explain that it is fiction, not biography, even though the three main characters "are based, vaguely, upon persons who once were alive." The illusion of authenticity is strengthened by the inclusion of real people -- musicians, mainly, of the early 20th century.

For the narrator, Caroline Maclaren, is the widow of a successful American composer; and the theme of the book is her experience of the wretched marriage that underpinned the public image: "History must be full of such alliances between famous men and their satellite, serving wives," Caroline says. "Their true persons and their inner lives are rarely known in the painful and almost faithless detail I have given here."

What gives the main part of this book its polish and flavor is the contrast between matter and manner. The matter is lurid. Young Caroline Newby marries Robert Glencoe Maclaren and soon learns that until her arrival Robert and his mother slept together in the mammoth four-poster, draped in yellowing lace, that she herself now shares with him. Later she discovers that her husband has a passionate relationship with another, male, musician. Why then did he marry her? To escape from the arms of his mother, after which he "floated free, wary, careful not to form another emotional attachment as exhausting and lengthy."

His need of Caroline is minimal; all his "physical prowess" goes into his music. He becomes increasingly successful, and Caroline increasingly lonely and introverted, until a mysterious illness makes him totally dependent on her in their Saratoga Springs farmhouse. We are then treated to a horrific but masterly account of the symptoms and management of a man in the tertiary, terminal stage of syphilis.

Caroline relates the most intimate and appalling happenings in an archaic, eclegant English that is full of echoes -- Poe? Hawthorne? The vocabulary is on occasion esoteric ("haptic," "tristful"), sometimes needlessly so, as when Caroline describes herself tautologically as "mouselike, murine." The dialogue has an oddly wooden sound, as if in translation. But the story up to Robert's death has an intensity that the arcane style seems only to reinforce. Grumbach can clothe the most modest perceptions in cultivated 18th-century prose rhythms which (and this is quite a feat) sound not at all pretentious, but graceful and musical.

But the upsetting thing is this: the book has a final third, titled "after-life," where in my opinion it falls on its nose and does not recover. After Robert's death Caroline discovers in herself a "profound love" for his young German nurse, Anna. This love -- "moisture to my dried roots" -- is consummated in the same great fourposter that supported the unions of Robert and his mother and of Robert and Caroline. They share an idyll, while administering the farm for the "Robert Maclaren Foundation" as a retreat for young musicians; but all ends finally in arson, death and desolation.

It is not, however, the accumulation of gothic catastrophe which is responsible for the to me disastrous loss of tone in this final movement. It is notoriously hard to write well about sexual happiness; and Caroline's accounts of bliss, and of Anna's "lissome, fineboned, full-fleshed body" are soft unto pulpiness. "Until Anna came," she says, "I had waited, prepared to be born," Which makes one suppose that, in the author's intention, the first marvelous two-thirds were but a preparation for this vegetable epiphany.

The point about Anna seems to be that she answers the life of the educated mind with a countervailing instinctual, earthy wisdom. Caroline reads Middlemarch aloud: "Anna countered my rolling literary sentences with her stepmother's wisdom about the best state in which to plant turnip seeds" (strak naked, apparently). Having been so exhilarted by the earlier narrative and by the insights delivered in Grumbach's own "rolling literary sentences," one longs' to beg Caroline not to abandon Middlemarch entirely for nude turnipplanting.

Anna's "pleasure in life is service," and she belongs to "the waiting classes, the pram pushers, the burden bearers up the sides of great mountains...." But Caroline too was a burden bearer, for Robert; if "service" is to be thus apotheosized, was she at fault in not deriving pleasure from it?Grumbach doesn't explain.

It is hard to believe that she conceived the book as a lesbian manifesto. For one thing, Anna comes so late that she shakes the structure. This may be "true to life," but it is risky in art. (Though to return to George Eliot: another life-bringer -- Eppie in Silas Marner -- does not turn up until well over halfway through.) The novel must rather be seen, much more simply and as Caroline herself describes it, as "a sketch of the chamber of one heart." But here reviewing ends, and argument begins: and one only argues over books that are provocative and worth-while, as this one is.