No, this is not the Confessions of an Illegitimate Child. Eleven-year-old Cynthia's parents aren't married any longer because they've decided to got a divorce--and as Cynthia comes to realize, they really are the Odd Couple: Daddy can't bear to have Cynthia and six-year-old Sara make a mess in his new apartment, while their easygoing Mom only straightens up when the cleaning lady's coming; and so on. Or, as she says after her (very funny) first date leads to others, including a brief liaison with likable but blinkered Bill: "" 'Can a liberal Democrat find happiness with a conservative Republican?' NO!"" So she won't marry Bill either--and will, eventually, wed poverty-clinic doctor Sam. Meanwhile Cynthia has made her own adjustments--most especially to Daddy's ""fat,"" ""yukky"" receptionist girlfriend Ellen, who manages to keep smiling even after Cynthia and Sara--in the book's one silly, unlikely episode--have conspired to color her teeth green. The author is a psychiatrist and she obviously knows whereof she writes (Mom is a model of insightful decisiveness when Sara's conflict-of-loyalties immobilizes her). The story could use a little more incident and a little less insight altogether, but for the most part it's smart and sassy without being Seventies-slick.