In Traitor King, Andrew Lownie shows how the Duke of Windsor — the former Edward VIII, who abdicated in 1936 — gave aid and comfort to his country’s enemies before and during the second world war. Reading this meticulously researched book, it seems extraordinary that he remained at liberty. A less deferential society would have interned him in 1940 along with the followers of his friend Oswald Mosley, most of whom were far less dangerous.