Effi Briest tells the story of a young Prussian girl in the 1880s, who marries a rising politician incapable of love, loses everything in the aftermath of a brief affair, and makes peace with leaving too brief a life early.

Seventeen-year-old, free-spirited Effi Briest lives happily in the quiet Prussian town of Hohen-Cremmen. She agrees to marry her mother's 38-year-old ex-suitor, a rising politician in Eastern Pomerania. Hectic preparations include shopping in Berlin for a trousseau. Honeymoon letters home show enthusiasm but little joy. Effi's delight at her new "oriental" surroundings in Kessin is brief. Innstetten and maid Johanna are uncomfortable talking about the upstairs "gallery," where Effi hears noises. When work takes the groom away, fear of a ghost debilitates Effi. Nevertheless, she adapts but is truly comfortable only with Gieshübler and his protégée, the singer Marietta. Effi knows that she is too young to become a mother, but Annie is born, cared for by Roswitha, who Effi rescues from unemployment and depression shortly beforehand.

Major Crampas comes to town, Innstetten's former comrade, a flirtatious gossip with a jealous wife. Crampas becomes a riding companion, first of Innstetten, then of Innstetten and Effi, and finally of Effi alone (albeit chaperoned). He talks obliquely of Innstetten's "mystical leanings" and being a "born pedagogue," wanting to improve Effi. After Christmas, Crampas and Effi begin an affair, during which Effi hears Roswitha's story about the youthful pregnancy that nearly destroys her life. Effi knows the danger of what she is doing, does not justify herself, but cannot stop. Only when Innstetten is transferred to Berlin is Effi delivered from Kessin and the affair. Effi adjusts to another new life, determined to be a good wife. They enjoy a vacation on the Baltic Sea, but Effi's parents sense something is wrong.

In Berlin over the next seven years, Effi is pursued by the shadow of her affair. At her mother's insistence, she takes the cure, and, while she is away, Annie, as wild as she, has an accident that results in Crampas' letters being discovered. Innstetten commits himself to the unwanted path of honor, and in the aftermath of the fatal duel, Innstetten does what honor demands, divorcing Effi and taking sole custody of Annie. The von Briests take his side. Roswitha alone sides with Effi, who again adjusts to a new life, until she happens to see Annie and becomes obsessed with meeting her. The reunion is tragic because Innstetten brainwashes the child into needing permission for anything. Effi now hates him for being so perfectly proper.

As her health continues to decline, Effi's parents resist social pressure and allow her to come home. Innstetten relents when Roswitha requests the one thing that Effi needs for the last summer of her life: Rollo. He has gotten over his obsession with work and honors but cannot find how to put his loveless life together. On her deathbed, Effi lets go of anger at him and accepts her fate, hoping that knowing this will help him, too. At her request, Effi is buried with her maiden name. Papa gets the final word: what could have been done differently is entirely too vast a subject to discuss.