In the early Puritan settlement of Boston, a young woman named Hester Prynne is led from prison to a public scaffold to be shamed before the town. She carries an infant in her arms and wears on her breast a scarlet letter A, elaborately embroidered by her own hand, the mark of her sentence for adultery. Her husband, long absent and presumed lost at sea, is nowhere among the crowd, and she refuses every demand to name the man who fathered her child.
On the scaffold the young minister Arthur Dimmesdale, beloved for his eloquence and apparent holiness, is made to exhort her to confess the father's name. She will not. Watching from the edge of the crowd is a stranger, an aging scholar, who is in truth her missing husband. He resolves to keep his identity hidden, takes the name Roger Chillingworth, and vows to discover the partner in her sin, telling her that no concealment can finally hide the man from him.
Hester settles at the edge of town and supports herself and her daughter, Pearl, by her needle. Pearl grows into a wild, bright, unaccountable child whom Hester often sees as the scarlet letter given life. Cut off from ordinary society, Hester serves the poor and the sick so faithfully that many townspeople begin to reinterpret her badge: where it once meant only adulteress, they start to say it means Able.
Chillingworth, posing as a physician, attaches himself to the ailing Dimmesdale and slowly confirms his suspicion that the minister is the father. He becomes a constant tormentor, keeping the wound of secret guilt at red-heat. Dimmesdale, unable to confess yet unable to forget, wastes away in private penance and a midnight vigil on the very scaffold where Hester once stood. When Hester meets him in the forest she casts off the letter for an hour, lets down her hair, and they plan to flee together, but the escape never holds.
On a public holiday Dimmesdale preaches his greatest sermon, then mounts the scaffold in daylight, takes Hester and Pearl by the hand, and confesses, baring a mark on his own breast before the people as he dies. Chillingworth, his purpose gone, withers away soon after. Years later Hester returns of her own will to the cottage and the letter she could have left behind, having made the badge a sign of counsel and mercy, and is at last buried near Dimmesdale under a single slate that bears the device of the letter still.