His Last Bow - Arthur Conan Doyle
On the eve of the First World War, Von Bork, a German agent, is getting ready to leave England with his vast collection of intelligence, gathered over a four-year period. His wife and household have already left Harwich for Flushing in the Netherlands, leaving only him and his elderly housekeeper. Von Bork's diplomat friend, Baron von Herling, is impressed by his collection of vital British military secrets, and tells Von Bork that he will be received in Berlin as a hero. Von Bork indicates that he is waiting for one last transaction with his Irish-American informant, Altamont, who will arrive shortly with a rich treasure: naval signals.