Irene’s growing intimacy with the architect Philip Bosinney provokes Soames Forsyte’s jealousy, a legal quarrel over the cost of Robin Hill, and—after Bosinney’s absence from his defence—Bosinney’s subsequent death (accident or possible suicide), which deepens the family scandal. Irene flees and later returns; Soames alternates between fury, shame and possessiveness, while old Jolyon, stirred to protect his grandchildren and unsettle the Forsyte order, alters his will and contemplates acquiring Robin Hill.
Jolyon Forsyte’s growing intimacy with Irene in Paris remains unconsummated and is rendered irrevocable by his son’s enlistment and death.
Parallel domestic crises—Dartie v. Dartie, Val Dartie’s impulsive engagement and enlistment, and Winifred’s legal and financial manoeuvres—disrupt the family equilibrium.
Soames pursues legal redress and remarries (Annette), while the Forsytes endure births, funerals and social shifts that expose tensions between possessive propriety and a changing age.
Irene's past—an unhappy marriage to Soames and a fatal affair—comes to light in Jolyon's confession and divides loyalties when Jon falls for Fleur, Soames's daughter.
Jolyon dies; Jon, persuaded by his parents' history, relinquishes Fleur and leaves with his mother, while Fleur marries Michael Mont.
Timothy's unexpected will and the funerals frame Soames's austere reflections on possession, class change and the waning Forsyte creed of private ownership.