A first novel--a sweet-and-sour scientific bedroom comedy reminiscent of Arthur Schnitzler's La Ronde--that's by a medical student at Harvard whose work has appeared in several ""Hers"" columns for the The New York Times, who writes a monthly column for Discover, and who is an absolute whiz at nailing down the mercury of love. Klass has an analytical bent second to none for plotting the recombinations of young married professionals passing through Splitsville in Manhattan. Her heroine, Anne Montgomery, is a researcher for a private lab in the recombinant DNA industry. Like her husband Kent, who has abandoned linguistics for banking, Anne has given up academia to go into applied research and spends her days rearranging genes into new sequences. As it happens, her attraction to lab technician Jason, with his 29-inch waist and heroic pelvic development, leads her into an unwanted recombination when she tells shocked, monogamous Kent of her affair and instantly deflates their marriage. Within days she's had to move out, tearfully joining her country cousin Louisa and her fellow roomie, a six-foot, knockout, pencil-thin model named Felice, in their apartment. Innocent Louisa's heart is divided between premature ejaculator Jim and stud physicist Yuri. Felice, 20, apparently a virgin but wise beyond her years about men, is utterly devoted only to herself and spends her days amid jars of creams and recombining her lush wardrobe with the skill of a chess wizard. Anne is now seeing Jason twice weekly, in her room, though he has to go home to his dancer girlfriend Jeanette each night. One night Anne Finds herself in bed with Yuri, whom she thoroughly dislikes but can't resist. Then with Jeanette's permission, she moves in with Jason and her, forming a weird mâ€šnage. Husband Kent meanwhile has taken in 19-year-old Jewish poet Emily, a young thing who adopts unwilling Anne as a shaman for handling Kent. As matters go on, Anne regularly dines with divorced fellow-researcher Charlotte, who is fantastically self-sufficient but unfortunately in love with a brilliant married doctor and father of three from Connecticut whom she has been seeing for two nights every two weeks for the past four years. At the same time, Anne and Kent's old friends, Alan and Margie, are splitting, and balmy Margie keeps barging in on poor old Kent and seducing him; and Alan (getting back at Margie?) barges in on Anne, grabs her by the breasts and tries to make love to her on the floor of her new apartment. . . All these wild changes--near-slapstick in the reviewer's telling but not in the novelist's--are detailed by the wicked eye of an inspired cultural anthropologist half-mad under a June moon. Anne's adventures in the lab are equally sparkling, and yet every metamorphosis of these educated but tormented butterflies is set down in marvelously clear bleached prose worthy of the New England Journal of Medicine. A gem.