Deft, spare, understated, subtle, disciplined, classic—these are the words critics have used to praise the novels of Françoise Sagan. She possessed to an uncommon degree, they said, the typically French flair for nuance. She could sketch in a character in a gesture, immortialize him or her in a line or two of dialogue. Her sentences were as well shaped as a Chanel suit. She dealt in essences, light and sensuous as a perfume. National pride preened itself on her, anxious to compare her to Colette, as if these two particular writers embodied something that was peculiarly and exclusively French. Now, in "Scars on the Soul," Miss Sagan has exposed the woman behind the novels and very nearly destroyed her own myth. The book is a very flimsy novella padded out by alternating chapters of "self-portrait" in which she talks about the writing of this work, about...