New Yorker Cornie Blume, 11, deals with the ups and downs of joint custody and the arrival of her father's new baby--as she shuttles between her mother's Broadway apartment and her father and new stepmother's home on the Upper East Side. Though complicated, the arrangements are cordial, and Cornie has adjusted--until her father announces that there's going to be an addition to the family, and her mother begins to receive brochures from realtors in southern California. After a rocky start, Cornie overcomes her jealousy and grows to love her new sister; she is also much relieved to learn that she won't be moving to L.A. Moreover, her musings on family life reap an added benefit: a topic for a school photo project. Hest's sympathetic, often humorous story has a hip, urban tone. She zeroes in on some of the anxieties of children caught between divorced parents, treating their concerns with the seriousness they deserve, while giving young readers a fine sense of what it's like to grow up in a big city. Entertaining and nourishing.