Effi Briest is an 1895 realist novel written by German novelist and poet Theodor Fontane. It tells the tragic story of a young Prussian girl named Effi Briest, who marries a German aristocrat who is twenty-one years her senior. After that, her life takes a turn for the worse, as she loses her innocence and her childlike free-spiritedness, her family, her health, and her husband and daughter.

The novel opens in Hohen-Cremmen, the hometown of the seventeen-year-old happy and naive Effi Briest. Attracted to wealth and social status, she agrees to marry Baron Geert von Innstetten—a thirty-eight-year-old politician and former suitor of her mother, Louise. Soon, the wedding preparations begin, and the pair moves to Kessin. At first, Effi is excited that she is finally able to leave her small hometown and live where the wealthy people live; however, her excitement slowly begins to die down, and she becomes extremely lonely and miserable. Her husband is often abroad, traveling for work, and leaves Effi all alone. Intimidated by her isolation, she begins a short-lived love affair with Major Crampas—a political rival of Baron von Innstetten, despite him also being a married man.

After some time, Effi gives birth to a daughter—Annie, and the family moves to Berlin. In the first few months, everything seems to be fine and well. However, one day, the Baron finds Effi’s letters to Major Crampas. Infuriated by his wife’s unfaithfulness, the Baron kills the Major in a duel, and decides to divorce Effi, taking sole custody of their daughter. Effi’s parents take his side and disown Effi, telling her that they refuse to be close with someone who brought shame and dishonor on the family.

Several years later, as Effi learns to adapt to a new life yet again, she meets her daughter and tries to get close to her, only to discover that her ex-husband has brainwashed Annie into thinking that her mother is a bad person. Realizing that she cannot change Annie’s opinion, Effi decides to stop trying to repair their broken relationship.

Soon after that incident, Effi’s health slowly begins to deteriorate, and she falls into a deep depression. When they see that their daughter has developed a "nervous disorder," the Briests decide to take Effi back home and care for her. In the end, she asks her mother to write a letter to the Baron in her name, expressing her regrets, her forgiveness, her yearning for love and reconciliation, and her acceptance of her fate. At her death bed, Effi asks her parents to bury her with her maiden name.