THE INFORMED AIR: Essays. By Muriel Spark. Edited by Penelope Jardine. New Directions. 286 pages. $24.95.

Muriel Spark is a theatrical, subversive writer who is wholly original. There's no voice in literature quite like hers. She paints a world where evil and stupidity are ubiquitous, but somehow one comes away from her novels fortified: they're so brisk and invigorating. She doesn't really hold it against her characters - or people in general - that they're ridiculous. They interest her, and she makes them interesting to us.

Spark once told an interviewer that she wrote "like an observer from another planet." The alien perspective and penchant for incongruity that are the hallmarks of her novels is everywhere on display in "The Informed Air," a posthumous collection of essays and occasional writings. It's a grab-bag, but reach in anywhere and you'll find something delightful.

With their scaled-back plots and caricatured personalities, Spark's books stray away from reassuring likeness to life or even realistic fiction. Something is always surprising and a little off. She's very funny.

The first section of "The Informed Air" is given to Spark's writings about her own life (other sections are classified as Literature, Miscellany and Faith).

She and her family emerge from these pieces as the kind of slightly off characters that might feel at home in her fiction. Spark grew up in Edinburgh, where her father was a skilled factory worker who came home covered in soot every day, bathed and changed into a suit for a night of dancing. Her mother drank a bottle of madeira a day to calm her nerves. They were gay, generous people.

"The Celestial Garden Party," a short piece from 2002, captures the family mood through her mother's hat fetish. Spark's mother could never pass a hat shop. A collection of "large, wavy-brimmed, shady and bedecked" hats - bought to wear to garden parties that never happened - stood ready, a testament to hope. Spark's own closet, full of "drifting chiffon," satisfies the same bright urge.

Writing about her craft, Spark is clear and unfussy. She likes outrageous behavior; she likes a good ending. When a journalist asks her to pick a book she would like to have written, she has no answer. Her own are the books she wants to have written. Writing them is so easy ("the easiest thing I have ever done"), that it feels like cheating. When she's writing a novel, things that would normally go unnoticed in the course of a day "simply present themselves as if they positively wanted to be in the book."

This kind of mystically available subject matter turns up in her books, where many characters are also writers. For inspiration, not envy, Spark reads two books continuously: Proust's great novel and the Bible, especially the Old Testament (for the "intrigues, thunderbolts, smiles").

Throughout, Spark circles back to Edinburgh, the place where, she says, she was first understood but also the place she escaped.

In "What Images Return," she writes, "It was Edinburgh that bred in me the conditions of exiledom. And what have I been doing since then but moving from exile to exile? It has ceased to be a fate, it has become a calling."

The dour Calvinism of her native town figures in Spark's search for its opposite in Italy, her adopted homeland. Look with her out the window of her flat in Rome ("Living in Rome") or follow her along the road from Arezzo to Cortona in Tuscany ("Tuscany by Chance"), and she will make you understand why for her Italy is where "mean thoughts are out of place."

The big moment in Spark's life came in 1954 when she converted to Catholicism, a spiritual move that freed her up artistically. Conversion for Spark was a dynamic process, instigated by her readings of Cardinal Newman and by a dexedrine-induced breakdown that sounds like something in her novels. She began having hallucinations and paranoid delusions centering on T.S. Eliot's play "The Confidential Clerk," believing Eliot was sending her messages and imagining secret codes in everything.

The final section of "The Informed Air" includes essays on Faith, a roomy category that includes thoughts on "the sublime Cardinal Newman," a hymn to the cat ("If I were not a Christian, I would worship the cat"), a consideration of "sacramental" writing in the pagan Proust, several forays into the Book of Job, and a short piece on heaven as a place ("Nor would I be content in a general place where all good souls are supposed to go. O God, imagine yourself seated in a celestial omnibus next to Billy Graham!").

Wherever she goes - Edinburgh, Italy, heaven - Spark heeds the lesson of her most famous character, Miss Jean Brodie: "There needs must be some leaven in the lump."

Reviewer Catherine Holmes teaches English at the College of Charleston.