Among the notes left by the great psychotherapist Carl Gustav Jung is an undated fragment: "A lady came to my office. She refused to give her name . . . what she wanted to communicate to me was a confession." Morris West has long meditated on this mysterious penitent, and so, he believes, had Jung. "I have always felt," West writes, "that Jung, writing in his later years, was still troubled by the episode."

What did the lady confide, and why should it, above all the painful and troubling tales heard over the years in Jung's consulting room, have bedeviled the famous doctor? Because, West suggests in this fiction, the lady's trouble came at a time of particular crisis for Jung and, in an eerie and dangerous way, mirrored his own.

The lady of West's invention is a fabulous creature, one Magda Liliane Kardoss von Gamfseld. Illegitimate daughter of an English duchess and a Hungarian nobleman, she was a horsewoman, linguist, physician, landowner, widow of a titled Austrian, failed mother, great beauty and even greater debauchee. A bizarre and amoral youth in an enchanted private world leads to an adulthood of wealth, opulence, travel and self-indulgence, and finally, at mid-life, to a terrifying cycle of sexual obsession, sadism and suicidal depression. In desperation, she takes the advice of an old friend from medical school and journeys to Zurich to consult Jung.

On the train, she distracts herself by reading Sherlock Holmes. West obviously intends us to compare the task lying before Jung and Magda with the painstaking deductions of Holmes and Watson. But, like many of the book's details, this one misfires, and West reminds us instead of the one unsatisfying creation in the Holmes corpus, the evil Dr. Moriarty.

Conan Doyle concocted the Napoleon of Crime for a specific purpose: to provide Holmes with an antagonist capable of doing him in. Moriarty was made to order for this purpose: he matches Holmes trait for trait--in every aspect but one. Unlike the sage of Baker Street, however, he never really lives as a character; instead, he exists as an idea.

And that's the trouble with Madga: she is fabulous in the wrong sense, "fictional, imaginary" as Webster puts it, a Napoleon of Obsession to test the great analyst's powers. But in the end, her mystery is not very mysterious, and she never comes to life as a woman--especially not as a woman of her time and place, belle epoque Central Europe.

The details of her life simply don't make much sense. Could a woman with her "defective birth certificate" and decadent appetites actually have gotten away with what she did: assorted--and sordid--love affairs, followed by a white wedding to the scion of an ancient noble house, with a first-class medical degree and a finishing school education thrown in for good measure?

And would a woman of her era have held the views she did and expressed them in so jarringly modern a voice? John Fowles in "The French Lieutenant's Woman" pulled off the difficult trick of telling a modern story through a Victorian sensibility. But much of Magda's daylong conversation with Jung sounds instead like "Donahue" in fancy dress, using the concepts--and the vernacular--of modern skepticism, narcissism, and psychiatric awareness, not the more formal manner of their own time. Jung, Freud and company were at the farthest fringe of thought in their own day; their ideas have only become commonplace in ours.

So Magda functions not as a person but as a plot device to permit West's exploration of certain themes--the line between good and evil, the nature of guilt and obsession, the curative power of redemption. And since Magda composes half the book, she proves an ultimately fatal burden. Her dreams and nightmares dovetail too perfectly with Jung's, diverging only at one point--and a point vital to West's didactic scheme and to Jung's dispute with Freud--the religious nature of the psychoanalytic cure.

To say that this book fails as an experience in psychoanalysis is not to say that it fails entirely. Read as a psychoanalytic thriller, it holds a certain interest. Magda's and Jung's sexual misadventures certainly keep the pages turning, while deeper ideas about psychoanalysis also turn over in the mind, even after the last page is read. But to touch deeply, a story about sin and redemption or madness and cure must involve real people in a palpable world, not made-to-order abstractions in a universe of concepts.