Edward Phillips Oppenheim: which book should you start with?

During the First World War, a German Zeppelin loses its observation car one night, and the car falls near a small town in Norfolk, on the English coast. The next day, a stranger calls on Philippa, Lady Cranston. Philippa's brother is a prisoner in Germany, and this man, who helped him there, brings her news of him. But the stranger serves the enemy, and he asks to live in the town under a false name. Torn between her duty to her country, her love for her brother and her attraction to this stranger, Philippa must choose. Told with elegance and suspense, this spy novel is easy to read in the language you are learning.

Mr Sabin, an old exiled French duke, lives happily in Massachusetts with his wife Lucille, until the day she disappears in New York. Anonymous letters, written in yellow crayon, order him to return home. The crayon is the mark of a secret society of European nobles, determined to halt the rise of the socialists. Mr Sabin follows Lucille to London, where the society is using her to influence a powerful minister. Alone, this old man stands up to a formidable organisation, amid elegant drawing rooms and political intrigue. Full of suspense, this novel is easy to read in the language you are learning.