BOOK REVIEW / FICTION : Diametrical Opposites Join for an Enduring Friendship : FATA MORGANA, <i> by Lynn Stegner</i> ; Baskerville, $22, 357 pages

In medieval legend, Morgan Le Fay often appears as a fairy with the power to create deceptive but startlingly beautiful illusions. Inspired by that character, “Fata Morgana” is the term used to described a strange mirage seen first in Italy, in the Strait of Messina between Calabria and Sicily, but now more generally applied to any dangerously alluring phenomenon.

In Lynn Stegner’s novel, the notion of Fata Morgana is incarnated in the personality of Dixie Darling, a rebellious but captivating girl in her early teens who befriends the narrator when they first meet at a Catholic boarding school. Even at 14, Susan Thatcher is stable, studious and conformist, Dixie Darling’s diametrical opposite. Susan comes from the sort of conventional family that has all but disappeared from contemporary literature; Dixie is the daughter of an exquisitely ethereal photographic model and her hearty policeman husband.

By 1981, when the two young women meet again for the first time since they emerged from St. Agatha’s and roomed together for a crucial summer, Susan has become a corporate lawyer and married a nature photographer: “a nice man, a gentle man, with a smooth and somehow too-familiar face, the kind you can’t easily picture when it’s absent.” Dixie Darling is in prison, close to the end of a nine-year sentence, though her crime is not revealed until the end of the book.

After eight years of struggling to put Dixie’s fate out of her mind and heart, Susan had begun writing to her friend, finally receiving a terse postcard saying simply “Sue--Dixie here--Saturday is visitors day--Bring change for the machines.” Kissing her husband goodby, Susan sets off on the long drive from her Monterey home to the Southern California jail where Dixie is incarcerated, a trip that becomes a journey into the past the two girls shared; a brief but hectic history culminating in the fateful post-graduate summer when they lived together in that tacky San Jose apartment and worked as waitresses in a coffee shop.

Delving further back to their school days, we revisit St. Agatha’s in the late 1960s--a progressive and challenging girls’ school in an idyllic Marin County setting. Susan thrives in this nurturing atmosphere, but Dixie Darling is an obvious misfit from Day One. Her vivacity is attractive but somehow uncontrolled and her reactions are quixotic. When the commuter train on which the girls are returning to school hits a woman on the tracks and the students recoil in horrified disbelief, Dixie merely comments that the victim “had great hair.” Though Dixie often seems curiously detached from life, she’s a witty and stimulating companion. The friendship between the two deepens; Dixie’s ebullience balancing Susan’s caution, though Susan’s restraint has virtually no effect upon Dixie’s impulsiveness.

Invited to Dixie’s surprisingly lavish house for the weekend, Susan witnesses the suicide of Dixie’s beautiful mother, a primal trauma that sends her already unstable daughter even further over the edge. “A bit wild” is no longer an adequate description of Dixie’s behavior, and by the time the two young women are out of school and living in San Jose, Dixie has become indiscriminately promiscuous and increasingly alcoholic. Still only 18, Susan finds herself playing the role of caretaker, until eventually Dixie’s frantic search for love defeats Susan’s best efforts.

Elusive as the mirage that serves as the title and central metaphor of the novel, Dixie remains an enigma, despite the narrator’s struggle to find the key to her behavior. The ravishingly beautiful mother, aloof and depressed, existing only in her photographic image, offers a clue but hardly a full explanation.

But if “Fata Morgana” doesn’t entirely succeed as a dual psychological study, it does display the author’s remarkable sensitivity to both the physical and emotional territory she has chosen as her setting.