The Forsyte family gather to celebrate the engagement of Winifred Forsyte to Montague Dartie, but Winifred's parents, Emily and James, disapprove. Soames Forsyte, a rich and successful partner in the family law firm, meets Irene Heron whilst in Bournemouth on business. She's penniless, but beautiful and accomplished and agrees to marry Soames after an aggressive courtship.

Soames is concerned about his marriage and hires Bosinney to build a country house at Robin Hill for Irene, bringing the couple together and they soon fall in love. After years apart, old Jolyon gets in touch with his son young Jolyon, who now has two children, Jolly and Holly. Dartie and Winifred's marriage is a success, but Dartie's love of fast living and gambling causes money problems.

Irene and Bosinney plan to run away together and Soames is furious that the project is overspending again and decides to sue Bosinney. But a tragic series of events - including rape - ensues from the night before the hearing which ends with an horrific death. But Irene's troubles are far from over as Young Jolyon makes a decision that will haunt him.

Grieving after Bosinney's death, Irene runs away, and Soames is left to pick up the pieces of his once-ordered Edwardian life. Old Jolyon reunites his family at Robin Hill, where, some years later, he happens upon Irene in a secluded part of the garden. She becomes a regular guest and they become great friends, and his pity and affection to her incences the family when his will is read after his death.

Its 1899, Montague Dartie is bankrupt after a big loss at gambling and steals Winifred's pearls, and threatens to shoot her when confronted. Soames is lonely and bitter about the past, and wants an heir: he has a suitable woman in his sights, Annette, but must first find Irene and divorce her. His asks for help from Young Jolyon, whose daughter Holly is attracted to Winifred's son Val Dartie. Soames attempts to coerce Irene, who escapes to France, where Young Jolyon finds her, and finds that they are attracted to one another.

Soames travels to Paris but is decidedly rebuffed by Irene, who has fallen for Jolyon; they are named in the divorce petition, and are soon parents to a son, Jon. Soames acquiesces to his father James, who is desperate for a grandson before he dies, by marrying Annette. But her pregnancy does not proceed easily, and Soames is forced to choose between the life of his baby and that of his wife.