Natalie Barnes, wife of Gregory and mother and college teacher, has been sitting in for years on the brilliant lectures given by Tom Rilling, husband of Barbara and father and art-maven. A hook-up is finally effected. The affair commences. Embarrassment, silliness (""He apologizes for giving offense, for taking it, for future sins, for sins not dreamed of, for peeling grapes""), exalted states of passion, trivialities-Schwamm's intellectually agile first novel is encyclopedic about the social details and up-to-dateness of sophisticated adultery. The plot (shaded with sentimental dips into Natalie's past via old diaries and death-bed realtionships among her Hungarian relatives) bears no greater scrutiny than does most romance fiction: Should they? (Yes); Do they? (A lot); Will it last? (Uh-uh). But in the ""adjacent lives"" of the lovers, the left-over husband and wife, the children, there is often the poignant guilt-love you find in good Updike. Schwamm's tendency may be toward brittle busyness, analysis, distance--at times Tom and Natalie seem like nothing else but stakes around which Schwamm's opinions vine. But through the cool, pat, ruffleless surface comes the affair's sad heat, the never-ending compromising, the little retreats--and all this has real punch. Not quite satisfying--nothing seems missing so much here as imagination--but still a worthy debut.