Francis Norgate is a junior British diplomat, stationed in Berlin in 1914 just prior to the outbreak of World War I. He is not a spy by trade, but becomes one through a series of accidents.
While dining with Baroness von Haase, Norgate is insulted by a Prussian aristocrat. After defending himself in the ensuing confrontation, Norgate ends up being recalled to London in disgrace. On his train journey home, he meets a jovial and garrulous German crockery merchant named Selingman. To Norgate's surprise, the conversation turns to Belgian fortifications at Liège. He then discovers a list of German spies stationed in Britain. Apparently, Selingman is more than he seems.
Back in London Norgate tries to interest Scotland Yard in the list and also shows it to a Cabinet Minister friend of his. But the British government is convinced that war with Germany is impossible. They have allowed the country's defenses to be run down and therefore they are determined to go on living in a fantasy world in which the peace-loving German Empire would never start a war.
Norgate decides to go it alone, determined to feed false intelligence back to the Germany through his contact with Selingman. He is now an unofficial double agent. His position is complicated slightly by the act that he has met the Baroness von Haase again and is hopelessly in love with her. She loves him as well, but it turns out she may also be a spy.
