A novel to amuse, baffle; Loitering with Intent, by Muriel Spark. New York: Coward, McCann & Geoghegan.

It's possible, I suppose, to try to describe a Muriel Spark novel without getting giddy; it's impossible to read this one without being amused, fascinated , and rather appalled.

The first time I read it, I was quite certain which strand was "real" and which strand was merely mirroring and brilliantly mocking the real. A second perusal left me with only a "real" beginning -- a short sparkingly clear interlude in the park, as real only as a bubble is real.

To summarize the plot would spoil the writer's joke and the reader's enjoyment. I think it's safe to say only that "Loitering" is about a young girl , Fleur, who is writing a novel and wringing every ounce of copy out of the people she meets.

"The process by which I created my characters was instinctive, the sum of my whole experience of others and of my own potential self," she says, as she pins down the characters of her unpleasant employer and the group of unpleasant eccentrics he is exploiting. The eccentrics, all ten of them, are members of "The Autobiographical Association," and it's Fleur's job to rewrite their life stories, jazzing them up as she goes. So she is inventing two lives for each of them: One set goes into the ghostwritten autobiography, one set into her novel. And then a third set begins to emerge, and readers move uneasily to the edge of their seats.

The trick is to spot the moment when "reality" stops supplying material for the nove l and the novel takes over.