Steel's latest plump Twinkle is about a nice, nice dad of three, and is filled with juicy, domestic head-bangers. Sarah and Oliver Watson (advertising dynamo) have been married 18 years, producing two teen-agers and a nine-year-old reared in a ""storybook"" town in suburban New York. But now Sarah, who'd chucked a writing career for all this, wants out. Oliver has it all. ""When do I get mine?"" demands Sarah, who then splits for Cambridge and a Harvard M.A. Poor Oliver. Daddy-ing-to-the-optimum and career don't mix, and troubles swarm in: his mother is dying of Alzheimer's, and, worse, 17-year-old Benjamin, a glory boy headed for the best colleges, drops out to care for featherweight Sandra, who's expecting his child. Oliver moves to Manhattan with the diminished family, while Benjamin honorably attempts to support Sandra on minimum wages. In the meantime, Oliver's good friend Daphne soothes Oliver's wildly grinding gears (nonsexually), and he has a frenzied affair with young Megan. Never a dull moment: Oliver's now-widower father begins courting; Benjamin's baby Alex arrives, and Sandra's out to cause crises. Then there's a move to L.A., along with a gloriously happy fade-out with another woman who chooses between career and coziness. Steel continues to do what she does very, very well. Stock by the yard.