WHILE INTERVIEWING Italian converts to Islam nine years ago, Mark Sedgwick, a British professor of Islamic history at the American University in Cairo, stumbled upon Traditionalism, a secretive movement whose adherents have since the late 1920s rejected the modern West because beliefs and practices supposedly transmitted from time immemorial have been lost. Since then, he has traveled from Casablanca to Paris to Tehran to Washington, D.C., in an effort to trace the influence of Traditionalism's founder, obscure French thinker Rene Guenon, on movements as disparate as Sufism, right- wing extremism in Europe, and comparative religion departments in American universities. The results are recounted in his new book, "Against the Modern World: Traditionalism and the Secret Intellectual History of the Twentieth Century" (Oxford). While his research may sound like the plot of an Umberto Eco novel, Sedgwick assured Ideas via telephone from London, "Nobody has taken a shot at me yet." IDEAS: After writing such works as "The Crisis of the Modern World" (1927) and gathering followers, Rene Guenon converted to Islam and retreated into solitude in Cairo.