The action opens in London, 1924–25, among a socially ambitious circle whose private lives collide with public spectacle. Central figures are Michael Mont, a young Member of Parliament advocating “Foggartism” (an old publicist, Sir James Foggart, supplies the doctrine); his fashionable wife Fleur Mont; Fleur’s father Soames Forsyte, a class‑conscious, bullying patriarch; Francis Wilmot, a modest American lodger; and Marjorie Ferrar, a brilliant, fast‑living granddaughter of the Marquess of Shropshire. Secondary players—Sir Alexander MacGown, Bullfry, Sir Lawrence Mont and various journalists and lawyers—populate salons, courtrooms and Parliament.

Michael launches a public programme—expanded home agriculture, air defence, and youth emigration—as practical remedy for unemployment. He experiments privately as well, housing three unemployed men and setting up poultry, but the venture is marred when Bergfeld, a German actor among them, kills himself and the press turns the affair into scandal. Meanwhile Francis falls passionately for Marjorie; after she spurns him, he contracts pneumonia and is nursed anonymously by Fleur, a secret that feeds later gossip and domestic strain.

The immediate crisis begins at one of Fleur’s fashionable salons, where Marjorie is overheard calling Fleur a “snob.” Soames, determined to defend his daughter’s honour, orchestrates a vigorous libel action. He gathers covert evidence, encourages press assaults on “modern immorality” (notably Perceval Calvin’s novel Canthar), and engages counsel to turn the trial into an attack on permissive society. Bullfry opens for the plaintiff; for the defence Sir James Foskisson conducts a relentless cross‑examination of Marjorie designed to show that her circle treats conventional morality as expendable. Pressed about lovers, immodest roles and literary tastes, Marjorie refuses to answer; Sir James exploits her silences and arranges that objectionable passages and a risqué play be read to the jury at lunch, sensationalizing the case as a test of “modern morality.”

The courtroom spectacle has immediate social consequences. Marjorie, shaken, admits privately to Sir Alexander a past liaison; their engagement collapses. Summoned by her grandfather, she learns the scale of her debts and accepts conditional help: she must return gifts, pledge to behave responsibly and strive to earn her living. Resolving to turn over a “new leaf,” she contemplates America or the stage.

Fleur suffers public diminution; at Bella Magussie’s rout her conspicuous presence provokes divided opinion and she vows to “go round the world.” Michael, torn between political commitments and his wife’s humiliation, hesitates to abandon Parliament; Soames unexpectedly offers to take Fleur abroad, and with Old Forsyte’s accompanying presence the crisis is settled. The episodes expose the collision of private liberty and public judgment, satirize the press and class anxieties, and force characters—Marjorie, Fleur, Michael—to redefine identities amid reputational peril and the brittle hypocrisies of interwar society.