On Sept. 29, a messenger hand delivered a six-paragraph letter to the office of Peter Chernin, president and chief operating officer of News Corp., the parent company of Fox News. The missive, with carbon copies going to Fox News Channel President Roger Ailes and two other top News Corp. executives, spoke in obtuse but ominous tones. Producer Andrea Mackris, 33, was identified simply as "a young woman employee of Fox." Bill O'Reilly, 55, was identified simply as "one of Fox's most prominent on-air personalities." Typed on the letterhead of Mackris attorney Benedict Morelli, the correspondence accused the cable TV star...