Visceral chills enliven the otherwise predictable path of Braver's second scientific thriller (after Elixir). Uber-yuppie Rachel Whitman worries about the teasing her slow-witted six-year-old son Dylan suffers at the hands of his brilliant playmate Lucinda at the fancy Massachusetts North Shore day care center he attends; worse, she fears that her college drug experimentation caused Dylan's deficiency. Seeing Rachel's distress, Lucinda's mother, Sheila, confides that Lucinda was much like Dylan until she was treated by Dr. Lucius Malenko at his exclusive Nova Children's Center to medically enhance her intelligence. Malenko's other patients include young Julian Watts, who works hours on end making exquisite pointillist paintings and has ground his teeth to nubs; Brendan LaMotte, who has a computer-like memory and deep emotional problems (he fantasizes about killing his grandfather); and Nicole DaFoe, who's sleeping with her history teacher and sabotages her academic rival to secure an important scholarship. Meanwhile, dogged police detective Greg Zakarian obsessively pores over the long-unsolved death of an unidentified little boy, even as another boy is abducted. This convoluted yarn works best when Braver keeps all his storylines in play, but as the plot unfolds, he focuses mostly on Rachel, whose worries about her son's failure to over-achieve make her the most conventional and perhaps least compelling of his characters. Still, he paints a rich tableau of creepy medical details and middle-class status anxiety and pulls off an explosive finale. Agent, Susan Crawford. National advertising. (Sept.)