Kim Philby's secret life is far stranger than any spy fiction. Its outline is well known. Recruited by the Soviet KGB at Cambridge in the 1930s, he made his way into the British Secret Intelligence Service (SIS), where, after a brilliant wartime career, he became head of its anti-Soviet section, then liaison officer in Washington with the CIA and FBI - revealing everything he learned along the way to his Moscow bosses.

He was in the running to become "C," chief of the British secret service, where the damage he could have done would have been incalculable. But following the defection of his fellow spies Guy Burgess and Donald Maclean, in 1951, Philby found himself under a hazy but persistent cloud of suspicion, and he himself eventually fled in 1963, just steps ahead of capture.

Before he died in Moscow in 1988, unrepentant and fulfilled, he had become a symbol in the West of Soviet-inspired treachery - an Englishman from a privileged background who had betrayed the entire free world. But, it emerges, this is only a glimpse of Philby's story.

Genrikh Borovik, a distinguished Russian author and playwright, persuaded the KGB to allow him to interview Philby in depth. The outcome was five hundred pages of transcripts of tape-recorded meetings, during which they discussed and analyzed every aspect of Philby's life. When Philby died, his masters further allowed Borovik unprecedented access to his personal KGB file. The result is an entirely new portrait of Philby that reveals how much he had previously managed to conceal.

And, perhaps of even greater significance, we at last have a picture of how the KGB recruited and ran its agents, and of a flaw at the heart of the service. This fascinating account of the man who was probably the most enigmatic spy in history poses questions of enormous importance about the world intelligence community and the morality and value of espionage.