Kathryn Harrison's newest novel, Envy, is a tale with two story lines: The first is an exhaustively titillating look at the sexual desires of Will Moreland, a New York psychoanalyst who can't sit through a session with one of his female clients without slipping into silent yet elaborate and obsessive fantasies.

The second is a fascinating examination of Will's unresolved relationship with his estranged twin brother, Mitch, whose deep red birthmark across half his face led him to a life of secret longings and jealousies until a final confrontation resulted in his disappearance on the eve of Will's wedding.

The problem with these dual story lines is that the two don't develop in tango, as more artful literature might; instead, the first story line is ultimately usurped by the second, leaving us to wonder whether Harrison - or her editors - recognized that a second, far more insightful novel had emerged and ultimately disconnected itself from the first.

Harrison opens Envy with the first story line, offering us glimpses of Will's increasing sexual obsessions, as well as his struggle to abate those fantasies, until Will has sex with a client in a lengthy scene about two-thirds of the way through the novel.

Although such spiraling desires might prove intriguing, particularly in the life of a psychoanalyst, Harrison's reliance on meticulous details with every sexual exploit is both tiresome and ultimately harmful to an otherwise intelligent and insightful novel.

As we begin to hear more about Mitch and realize the intricate ways he had entwined his life with Will's, unbeknownst even to Will, the sex scenes only interrupt Harrison's development of such human emotions as insecurity, love, jealousy, longing and even spirituality.

We never meet Mitch, but his presence is increasingly tangible as the novel unfolds and Will begins to question his own sense of what was actual and what was untrue in his past.

In Harrison's favor, she intriguingly suggests that Will's relentless quest for sexual intimacy is an attempt to assuage a painful hole left vacant by unanswered spiritual longings. Will describes himself as "a tortured agnostic" who is prone to "spasms of private, even desolate, self-examination." Will is an intelligent, successful man with a fulfilling marriage and good friends, but he is painfully and decidedly empty, even in the midst of his achievements:

"Alert to coincidence and unanticipated symmetry, to aspects aligning in patterns, almost readable, he sifts, sorts and turns the pieces, lays them down and picks them up in what amounts to an endless game of mental solitaire, occasionally drawing close to something that comes out neatly and looks like a grand and universal plan, a sequence of details in which, as the saying goes, God resides. Summoned to his door by a pair of canvassing Jehovah's Witnesses, Will not only accepts the literature they press into his hands, he reads it. Accosted on his own corner by a canvassing flock of young Lubavitchers who demand to know if he's a Jew, he stammers in confusion, receiving the question as a challenge to him, him in particular, rather than the proselytizer's customary preface. He's not so much godless as God-bereft."

Unfortunately, the wisdom of passages similar to the preceding one is too often overshadowed by sex and, more importantly, by a novel that presents itself as a singular tale and yet begs to be refocused and channeled toward an emerging story line that, unlike the first, is astute and thoughtful, haunting and resonant.

Envy

• By Kathryn Harrison. Random House, 320 pages, $24.95.

• Grade: C

Jennie A. Camp's reviews and short stories have appeared in Prairie Schooner, Colorado Review and other publications. She lives in Platteville.