The Double Traitor (Unabridged)

The setting is the years prior to the outbreak of World War I. It is a time when Germany is outwardly preparing for war but Britain continues to believe it is invincible and that no one would challenge her. A vast German spy network flourishes in England, often in plain view. The main character is Francis Norgate, an aspiring British diplomat who falls in disfavor with his superiors for defending a woman while stationed in Berlin.
The resulting scandal causes Norgate to be recalled. On the way home, he meets a German gentleman, Selingman, who claims to be a crockery salesman. But, Selingman is not what he appears to be. Disillusioned by the English government, Norgate allows himself to be recruited by Selingman.