When devouring this thriller about Kim Philby, the high-level British spymaster who turned out to be a Russian mole, I had to keep reminding myself that it was not a novel. It reads like a story by Graham Greene, Ian Fleming or John le Carré, all of whom make appearances, leavened by a dollop of P. G. Wodehouse. But, in fact, “A Spy Among Friends” is a solidly researched true story. The London journalist Ben Mac­intyre, who has written nine previous histories chronicling intrigue and skulduggery, takes a fresh look at the grandest espionage drama of our era. And like one of his raffish characters relaxing around the bar at White’s, that venerable clubhouse of England’s old boys’ network, he is able to play the role of an amusing raconteur who can cloak psychological and sociological insights with dry humor.

The story of Philby and his fellow Cambridge University double agents has been told many times, most notably by Phillip Knightley and Anthony Cave Brown, as well as by Philby himself and two of his four wives. Macintyre, who draws on these and other published sources, was not able to pry open any archives or uncover startling new revelations. Instead, he came up with a captivating framing device: telling the tale through Philby’s relationship with Nicholas Elliott, a fellow Cambridge-educated spy who was, or thought he was, Philby’s trusted friend. In doing so Macintyre has produced more than just a spy story. He has written a narrative about that most complex of topics, friendship: Why does it exist, what causes people to seek it and how do we know when it’s real? The world of upper-crust young Englishmen provides a rugged yet rewarding terrain for such an exploration. Taught on the playing fields of Eton to shield themselves from vulnerability, they mask their feelings for one another with jokes, cricket-watching, drinking and “a very distinctive brand of protective dishonesty.”

Macintyre also takes on a related subject: the tribal loyalties of the inbred social class, on the fraying fringe of Britain’s aristocracy, that nurtured such friendships, both real and feigned, and created the boys’ club that populated its foreign, colonial and intelligence services. Members harbored, Macintyre writes, “a shared set of assumptions about the world and their privileged place in it.” While watching the races at Ascot one day, Nick Elliott mentioned to a diplomat friend of his father, who was the headmaster of Eton, that he would like to be a spy. “I am relieved you have asked me for something so easy,” the diplomat replied, and Elliott was soon ensconced at MI6, Britain’s counterpart to the C.I.A.

Kim Philby had the same desire, and he was recommended by the deputy head of MI6, Valentine Vivian, who had served as a colonial official with Philby’s father. Even though the younger Philby had dabbled in Communist circles while at Cambridge, there was little vetting other than Vivian’s asking Philby’s father about it over drinks at their club. “Oh, that was all schoolboy nonsense,” the elder Philby replied. So Vivian had him hired. “I was asked about him and said I knew his people.”