By the author of the cute geriatric Sadie Shapiro series: a celluloid-smooth tap of the Kramer vs. Kramer motherlode--as an urban Manhattan male mired alone in the complexities of fathering (in this case a grieving widower) pulls himself and his family together. Wine-firm exec Paul Klein, married 18 happy years to tiny, quite perfect Jane, wakes one morning to her sudden death of brain aneurysm. So, doggedly, Paul attempts to hold onto his family--pretty 16-year-old Hilary and solemn ten-year-old Bobby. Schedules are raggedy; Paul just can't do things ""Mom's way""; there are those problems that a mother should handle--like Hilary's heavy necking with slovenly boyfriend Peter or Bobby's tortured silences. But somehow, months later, Paul's pain seems to be ""draining away."" And, determined to see that the three get on with their lives, he issues an edict: ""the mourning is over."" He even accepts a date with a divorced neighbor (a good-natured failure at sex brings a closer palship). So then. . . enter: tall, shapely Ruth Golden, partner in a small live-wire ad firm. True, Paul catches fire for heavy dating. (""Go ahead,"" says wee gloom-and-guilt machine Bobby. ""Enjoy yourself."") But sex and Ruth are essential, and Paul brings Ruth to lane's house as his wife, as the children's step-mother. ""She's a phony,"" says Hilary. ""You're trying too hard, Ruth,"" says Bobby. And poor Ruth tries presents, loving, even cooking (which she hates). But only when Ruth explodes and starts packing do things get shaken up--with a final move from Jane's house to a brand-new condo. Natty patter (Paul's a perfect Alan Alda role), appealingly familiar character types, and the ever-hot stepmother issue: classic movie material--and very nice reading too.