Desplechin displays an ear for subtlety in her fine debut novel about two Parisian women, one a practical, driven single mother of two, the other a young recovering drug addict with a besmirched past. The unnamed narrator, a successful freelance corporate writer, meets Olivia through mutual friends and hires her as a live-in babysitter, although Olivia still dabbles in drugs and is emotionally unhinged. The narrator becomes fascinated by Olivia, worrying over her, protecting her and marveling at the things Olivia says and does. ""I can't get Olivia's stories out of my head,"" the narrator admits. ""My boundaries, my distinctions between the honest and the criminal are gradually being lost in a fog of confusion."" In this confusion, the story takes a riveting 180-degree turn. As Olivia begins to get her life together, the narrator lets her own fall apart. To her credit, Desplechin never dramatizes or moralizes; neither woman comes off as a saint or a sinner. Instead, Desplechin treats the material with a light touch that's sympathetic to complexities. A bestseller in France, this comic novel cleverly outlines what it takes the narrator almost a year to conclude: ""Thanks to Olivia,"" she remarks, ""I understand that good is not the opposite of night, white is not the opposite of black. It's more and less simple than that. Olivia's genius saunters through the territory of goodness, whistling."" (Feb.) Forecast: A charming, Matisse-like jacket may catch the eye of readers who enjoy sophisticated European relationship dramas in the vein of Tim Parks or Helen Dunmore.