Book excerpt: On May 16, 1948, the body of CBS correspondent George Polk was found floating in Greece's Salonika Bay, where he had been stationed to report on a bloody civil war. The murder was allegedly solved, but Kati Marton has conctructed a vivid, convincing account of who really ordered the assasination of George Polk - and the motive behind it. This is the story of a peculiarly American hero whose blunt honesty and idealism proved insufficient aids in traversing the trecherous grounds of Cold War politics.