Kim Philby was the most notorious British defector and Soviet mole in history. Agent, double agent, traitor and enigma, he betrayed every secret of Allied operations to the Russians in the early years of the Cold War. Philby’s two closest friends in the intelligence world, Nicholas Elliott of MI6 and James Jesus Angleton, the CIA intelligence chief, thought they knew Philby better than anyone, and then discovered they had not known him at all.