Effi Briest, who is attracted by social status, moves to the fictional Pomeranian port of Kessin (loosely modeled on Swinemünde). Her husband Innstetten is away for weeks at a time, and Effi, who is shunned by local nobles, finds but one friend. Her suspicions that their house may be haunted are not entirely laid to rest by Innstetten. When she says there may be a ghost, he derides her fears. The scorn he would bear if people knew of her terror would stall his career; hence his angry reply.
When Major Crampas arrives, Effi cannot help relishing his attentions despite Crampas being a married womaniser, and their love is consummated. Her husband looks down on Crampas, whom he finds a lewd philanderer with cavalier views of law. Crampas views Innstetten as a patronising prig.
Years later, Effi's daughter Annie is growing up, and the family moves to Berlin due to Innstetten's ascent. All seems well, but when Effi's letters to Crampas are found by her husband, he decides to divorce her. He gets custody of Annie and influences her to disdain Effi. When Effi and Annie meet briefly some years later, it is clear the two are estranged, and Effi stops trying to establish a good relationship with Annie.
The Briests disown Effi, thinking it ill behooves them to deal with someone who tarnished their name. Innstetten tells Crampas he wants to duel; he agrees and is killed by Innstetten. But the halcyon days of Innstetten's past life are over, and career success fails to delight him.
Effi's parents take her back when she becomes the victim of nervous disorder, depression. Facing death, she asks Luise to tell Innstetten about her regrets and willingness to forgive him. Her death forms a rather symmetrical ending that matches the novel's start. In the end scene, her parents vaguely concede guilt for her fate without daring to question the social canons that sparked the tragedy, citing the German maxim, "That would be too wide a field" (ein weites Feld).
