Somewhere in France - Richard Harding Davis

When Captain Henri Ravignac married Marie Gessler, he was mistakenly thinking she was French. But Marie is in fact German, and her command of the French language and culture makes her a perfect spy. At the first opportunity, she double-crossed Captain Ravignac and stole valuable documents from him, which makes her a great candidate for espionage when World War I breaks out. Travelling with the documents of Countess d'Aurillac, she moves behind enemy lines, but the life of a spy is typically turbulent and short... - Summary by Carolin