The story of the group of men who became known as the Cambridge Spies is one of the most extended and most extensive cases of Western nationals spying on their own government in the twentieth century. The principal persons involved -- Guy Burgess (1910-63), Donald Maclean (1915-83), Anthony Blunt (1907-83), and "Kim" Philby (1912-88) -- worked on behalf of the Soviet Union throughout World War II and the early Cold War era. Their activities were only very gradually uncovered and the full story has been even more gradually revealed to the public. The opening of the KGB archives in Moscow after the fall of the Soviet Union seems to have brought the exposures to their conclusion -- but there is no saying whether further information might be revealed in years to come. Although a number of other persons were connected with this group's spying on Britain and, less directly, the United States these four had, as far as is known, the most significant roles of the men who were recruited by the Soviets in the 1930s. Soviet intelligence worked from a long-term plan to develop "moles" who would infiltrate Britain's intelligence, government, and diplomatic services. The extraordinary success of the spies (as, it seems, the Soviets intended) was predicated on their membership -- on the basis of birth and education -- in the nation's elite managing/ruling class. The shocks that accompanied their unveiling forced a fresh look at the relatively unquestioned assumptions that allowed such a class-based system to flourish to the point where reliance on family background and schooling seemed to relieve security operations of the need for the proper checks and controls that should be standard operating procedure to protect against espionage. The successive scandals also did permanent damage to Britain's standing as an international power and to the "special relationship" enjoyed by that nation and U.S. intelligence services. Despite all its effects...