It's that time again -- middle age and the twenty year itch -- nothing new or very different, certainly, when Robert Merriwether, a doctor and scientist at Harvard who has until now put up with a sexually lackluster marriage, falls in love with a student, Cynthia, his daughter's age. ""Paranoiac radiance"" which extends from weekends to a summer in France and finally to the divorce. At this point one becomes less impatient and more involved with Merriwether during the partitioning of the past -- the house, belongings, etc. -- and one wonders whether any of them will be more than ""haphazard"" survivors. Stern, usually an astute writer, is here less at ease with the language of youth (""It's so quaint. So sweet, so historic-hysteric"" -- that's Cynthia; or passion -- her body ""innocent as a volleyball"" -- that's Merriwether) further tripping over self-consciously cranky words (lustrum; lordotic). Even at Harvard they might stick out like sore academic thumbs.