The Beatles, Carnaby Street, mini-skirts. But the new mood hasn’t reached the drab and fearful corridors of MI5 and MI6. Many agents joined the secret service to fight the Nazis. Now they are locked in a Cold War against the Russians. And some of them are traitors. The service has been shaken to its core by the high-profile defections of Cambridge-educated spies Burgess, MacLean and now Philby. Appalled at such flagrant breaches of British security, the Americans are demanding a rigorous review. Harry Vaughan is brought back from Vienna to be part of it. The Chief asks him to join two investigators – Arthur Martin and Peter Wright – who are determined to clean out the stables, and the first target of their suspicions is the Deputy Director General of MI5, Graham Mitchell.