Kim Philby, the so-called Third Man in the Cambridge spy ring, was one of the Cold War’s most infamous traitors. He was a Soviet spy at the heart of British intelligence, joining Britain’s secret service, MI6, during the war, rising to become head of the section tasked with rooting out Russian spies and then head of liaison with the CIA. Philby betrayed hundreds of British and US agents to the Russians and compromised numerous operations inside the Soviet Union. Protected by friends within MI6 who could not believe the service’s rising star was a traitor, he was eventually dismissed in 1951, but continued to work for the service surreptitiously until his defection in 1963. His admission of guilt caused profound embarrassment to the British government of the day and its intelligence service, from which neither fully recovered. Tim Milne, Philby’s close friend since childhood and recruited by him into MI6 to be his deputy, has left us a memoir that provides the final and most authoritative word on the enduring and fascinating story of Kim Philby the legendary Soviet master spy. It is a riveting read, with new detail on Guy Burgess and Donald Maclean, two other members of the Cambridge spy ring, and on Konstantin Volkov, the would-be KGB defector who was betrayed by Philby, one of several hundred people who died as a direct result of Philby’s treachery. **Tim Milne** retired from SIS in October 1968 and never spoke publicly of his friendship with Kim Philby.