Nira and Adlai, Jerry and Claire (separated), Penny and Cal--those are the couples in 1970. But then Nira, mother of Heather and Posy and baby Jasmine, waggles a flirtatious petal or two at earnest, family-loving molecular biologist Jerry (he has the care of daughters Jane and Stacy). And, as we learn when Klein bounces back and forth between '70 and '80, Jerry will marry Nira. . . while her English hubby Adlai decamps to remarriage in the Old Country. Meanwhile, circa 1980, Jerry's also having an affair with editor Penny, who's handling his pop-smash book about a scientist. (Her husband, self-centered actor Cal, is a perennial bed-hopper.) And Nira's hardly a homebody, with a heavy career as a clothes designer. Still, she and Jerry have a ""firm marriage"": it's Jerry who pulls Nira through after daughter Posy drowns in an accident. So what will Penny do when a baby is imminent? Is it Cal's or is it Jerry's? All ends happily, however--with Penny wisely keeping mum about the baby's possible dad, Cal coming through as a father (and husband), and Penny realizing to her embarrassment that Nira is a ""nice person."" Lots of double-martini asides on the troubles women have with men (""Wives become mothers, girlfriends become wives""), plenty of bed-sheet chat, likable kid talk: an easygoing, low-calorie, marital rick-rack and yack-yack for Klein's loyal following.