In a compelling first novel, 'A Certain Slant of Light,' Margaret Wander Bonanno has created a strong and vivid character who will evoke memories of real-life counterparts for many readers.

Sarah Morrow, failed nun but full-blooded woman, rebel and medieval scholar, is that authority figure who first challenged our basic assumptions about ourselves and the universe.

Unfortunately, that figure and its challenges too frequently recede with the passing years, becoming little more than a nostalgic blur rather than continuing to shape and influence current choices.

What if, through an entirely credible set of circumstances, that authority figure from the past returned? How would we be judged for what we've chosen to do(or not to do)with our lives? How would we be graded for the promises we failed to keep?

These are the questions that rivet a reader in this fascinating story of friendship between Sarah, now an aging college professor struggling to regain her full powers after a disabling stroke, and Joan, her former student, whose eight-year marriage has just ended, leaving her with a 3-year-old son and no financial or spiritual resources.

Joan calls on Sarah out of sympathy, an action sh immediately regrets when Sarah asks her to spend the weekends reading to her. Though she has regained most of her verbal powers since the stroke, Sarah still cannot recognize words on the page. This disability threatens to force her into an early retirement from her teaching position at a small Catholic college.

Joan, though resenting her weekend task at first, gradually comes to rely on the relationship. The two women read and talk and Joan discovers to her surprise that 'big words were starting to occur to her, a pleasant sensation after years of talking to babies and drunks and supermarket clerks.'

'Joan remembered that there had been time, not too far past, when she'd been considered intelligent. It was nice to feel that way again.'

They share memories of the men who were part of their lives: Sarah was married to a talented, roughhewn sculptor 17 years her senior whom shehas never stopped loving though he has been dead for many years; Joan drifted into marriage because she was tired of being a virgin and had been told she had no talent for her one ambition - ballet.

A crusade to have Sarah reinstated at the college provides the narrative skeleton for the novel, bringing an array of colorful supporting characters into conflict, but the evolving relationship between the two women is the heart of the book.

At the story's conclusion, Sarah gives Joan the intellectual confidence and financial means to start law school by suggesting that she and her son share her home. Joan hesitates, then decides the suggestion is worth a try.

"Where is it written," she asks herself, "that two unrelated women of different generations cannot live harmoniously in the same household?"

The arrangement seems to be working-for all of them. "It is only possible," Joan concludes, "to live happily ever after on a day-to day basis."

In the theater today the three-act play is virtually an anachronism. An expository first act has been abandoned in favor of a two-act form which involves an audience immediately in the dramatic conflict. Contemporary fiction could profit from employing this economy. It is 109 pages into this 357-page book before the two women meet, and the wait, though ultimately worth it, is too long.

In an interview, the author agreed with John Gardner's assertion that fiction should have a moral purpose, should seek "to improve life, not debase it." It is in this respect that "A Certain Slant of Light" deffers from Mary Gordon's "Final Payments," despite the similarity of the provincial Catholic backgrounds from which both books' characters emerge. In "Final Payments" the church is a crippling and repressive authority, forcing its protagonist into a perverted, life-denying choice before she finally frees herself of its influence. The two women in "A Certain Slant of Light" find the church equally outmoded as an institution but recognize its its historical function and build on it, in the same way that Sarah, while thoroughly modern in her attitudes, values the unique contribution of medieval man.

Her purpose in writing the book, the author says, was to show that "a strong person can hold her own against all possible adversity." It is a message that needs stating in today's world, especially for modern women emerging from their own Middle Ages, and "A Certain Slant of Light" proclaim it with originality and eloquence.