By Gabriel Schoenfeld, W.W. Norton & Co. Inc., New York and London, 309 pages, $27.95

Just a few weeks ago, on June 9, the U.S. Court of Appeals for the Second Circuit reversed a district judge’s ruling that the City of New York must disclose the police department’s file on its surveillance, preceding the 2004 Republican National Convention, of suspected trouble-makers. That unanimous decision testifies to the enduring relevance of Gabriel Schoenfeld’s “Necessary Secrets.”