Effie Briest by Theodor Fontane (1894)

I read this after seeing it on a Facebook friend's list of seven books that influenced her.  I have never heard of it, and found that it has a circle of respect in German literature.  Thomas Mann said that the author was the best German author since Goethe, and since those are the two German authors that I have read a fair amount of, I tried this and liked it very much.  It is a strangely feminist book, in the same vain as Anne Bronte's The Widow of Wildfell Hall kind of feminism.
The book is considered to be the greatest work of Prussian realism and certainly one of the best tragic novels of the 19th century. The story is simple enough and hardly unique: Geert von Innstetten, an ambitious nobleman and civil servant on the brink of middle age, makes an uncontroversial marriage to Effi von Briest, the 17-year-old daughter of a former flame. Innstetten takes her back to the town in Pomerania from which he runs the local administration. A daughter, Annie, is born, but Innstetten is keen to get on, and leaves his young wife on her own where she falls prey to a womanizer, Major von Crampas.  The subsequent story is also in the end predictable, but plays out in an unusual manner.  Well worth reading.