Disbelief is the instinctive reaction to the double life of Anthony Blunt. One of the sons of the quite conventional chaplain of the embassy church in Paris. Attentive to his mother. Marlborough and Cambridge. Frequent long spells in France and Germany, fluent in the languages. Art historian and homosexual. Surveyor of the Queen’s Pictures, a natural for the Queen Mother’s circle. This is close to a novelist’s parody of a certain sort of highbrow career. And then betrayer of all that reassuring English stuff in favor of Stalin, foulest of murderers. The man, the Establishment he adorned, the country in...