The Forsyte family gathers to celebrate the engagement of Winifred Forsythe to Montague Dartie. Soames Forsyte, a rich and successful partner in the family law firm, meets penniless but beautiful and accomplished Irene Heron. Young Jolyon, who is in love with his children’s French governess, Helene, decides to leave his wife, cutting himself off from the family and forfeiting his fortune.

Irene has agreed to marry Soames. Two years later, Soames, concerned about his marriage, hires architect Bosinney to build a country house at Robin Hill for Irene. Bosinney is the husband-to-be of June, daughter of young Jolyon Forsythe. Young Jolyon is surprised when his father, old Jolyon, gets back in touch.

Irene and Bosinney fall in love. With the exception of June and Soames, the entire family seems to know about the affair. Soames is furious when the house costs more to build and decides to sue Bosinney.

Irene and Bosinney spend time together, and when she comes home late, Soames takes advantage of her unlocked bedroom door and rapes her. When Irene meets Bosinney the next day, he’s furious. As he runs through the foggy streets to confront Soames, he’s hit by a cab and killed. Old Jolyon reunites his family, and they buy and move to Robin Hill.

Irene leaves Soames for good, leaving behind everything, including her wedding ring. June and her father, young Jolyon, reunite. Soames is in a deep depression. Five years pass, and Helene (the French governess) has died. Old Jolyon meets Irene by chance and they become friends.

Old Jolyon dies. To the astonishment of all, he has left Irene some money. Twelve years pass. Soames marries Annette, a French woman. Dartie is gambling recklessly and cavorting with prostitutes, embarrassing the family.