The Age of Innocence is set among the wealthy, closely related families of New York in the 1870s, a world where descent, manners, and reputation matter more than money or law. Newland Archer, a young lawyer of impeccable standing, is newly engaged to May Welland, a beautiful and conventional girl who embodies everything his set admires. He looks forward to a settled and approved life.
Into this ordered world returns May's cousin, the Countess Ellen Olenska, who has left a cruel European husband and now wants to live independently in New York. Her foreign manners, her honesty, and the whiff of scandal around her unsettle the family. Archer is first asked to defend her on the family's behalf, including to talk her out of seeking a divorce, and in doing so he is drawn to a way of seeing that makes his own life look narrow and rehearsed.
Archer and Ellen fall in love, but every path to each other is blocked by duty and by the watchful kindness of the people around them. To escape his own feelings, Archer presses May to marry him sooner, and the wedding goes ahead. Marriage does not settle him; it sharpens his sense of being held in a system of polite signals where the real thing is never said aloud and where everyone seems to know more than they admit.
The pull toward Ellen continues after the marriage, building toward a break that never quite comes. The family, sensing the danger without ever naming it, arranges for Ellen to return to Europe and stages a farewell dinner that looks like generosity. Only at that table does Archer grasp that he has been quietly managed all along, and that May, by means he barely understands, has secured her marriage. Soon after, May tells him she is expecting a child, and the matter is closed.
The final chapter jumps forward about thirty years. May has died, the children belong to a freer and more open generation, and Archer, now a widower of fifty-seven, travels to Paris with his son and has the chance to visit Ellen at last. He chooses instead to sit on a bench below her window and not go up. The renunciation that shaped his youth is renewed by choice, and the book ends on the cost and the strange dignity of a life lived inside its limits.