THE nonlinear narrative tradition is apparently infectious this fall. Riot: A Love Story (Arcade, $24.95), by Shashi Tharoor, the acclaimed novelist and interim head of the United Nations' Department of Public Information, exhibits his appreciation of Rashomon by using newspaper clippings, interviews, writen correspondence, and personal memories to reveal the explosive story behind the death of an American woman in Northern India. After a brief stint living in India with her family ten years before, twenty-four-year-old NYU doctoral candidate Priscilla Hart returns to the troubled nation as a starry-eyed volunteer for a population-control awareness program. When she is killed amid the violence of Hindu-Muslim rioting, her divorced parents come together in search of answers, only to surmise that her death is more deliberate and political than they initially realized - the possible result of local resentment for her work with abused women and her clandestine affair with a married district magistrate.