I am sorry to read of Captain von Rintelen's death.
I always thought The Dark Invader as good of its kind as any book that came out of the First World War, or for that matter out of the second. The story of von Rintelen's sabotage of British munition-ships sailing from American ports, thanks to a delayed-action device which started fires after several days at sea, is effectively and objectively told. So is the story of contacts with von Paprn, the future Chancellor, then Military Attaché at the Embassy. in Washington. So is the story of von Rintelen's association with the voyage of Sir Roger Casement to Ireland in a German submarine. So is the story of the faked telegram which brought von Rintelen back to Europe, his removal from the Dutch liner at Folkestone, his con- frontation with Admiral Sir Reginald Hall (" Smiler" Hall), head of the British Intelligence Service, his subsequent internment at Donnington Hall, and his enduring friendship with Admiral Hall. It is as good a piece of reading as any of John Buchan's romances, it has the additional merit of being (to the best of my belief) true, and the additional merit of demonstrating that one of the cleverest of German secret agents was not quite clever enough to outwit the British Intelligence Service.