When Kim Philby fled to Moscow in 1963, he became the most notorious double agent in history. A British intelligence agent since World War II, he had risen to become their chief officer in Washington. Exposure of other double agents led to the revelation that Philby had been working for Russia longer than he had been part of MI6. Now Robert Littell recounts the early years of this fascinating, flawed man who kept people guessing until the very end.