Effi Briest by Theodor Fontane
Unworldly young Effi Briest is married off to Baron von Innstetten, an austere and ambitious civil servant twice her age, who has little time for his new wife. Isolated and bored, Effi finds comfort and distraction in a brief liaison with Major Crampas, a married man with a dangerous reputation. But years later, when Effi has almost forgotten her affair, the secret returns to haunt her, with fatal consequences. Considered to be Fontane's greatest novel, Effi Briest is a humane, unsentimental portrait of a young woman torn between her duties as a wife and mother and the instincts of her heart.