The sleuth who lives in a large house in St. James’s Square, London, is Sir Henry Marquis, head of the Criminal Investigation Department of Scotland Yard. He also owns a country mansion and a villa on the French Riviera and internal evidence suggests he was educated at Rugby’s famous public school and Oxford University. He previously ran the English secret service in the India-Burma border area and had also been busy in unspecified places in Asia, although there is reason to suppose he is familiar with Mongolia. Sir Henry belongs to the Empire Club in Piccadilly and apparently goes to the opera now and then.