The year is 1642. Hester Prynne, a young wife whose husband has been missing for over a year, is accused of adultery following the birth of her infant daughter Pearl. In a shameful public ceremony, Hester is forced to stand on a scaffold for more than three hours and submit to an interrogation. She refuses to reveal the name of her child's father, which angers the Puritanical citizens of Boston. She is forced to wear a scarlet-colored A on her clothes to mark her as an adulteress.
While on the scaffold, Hester sees her husband, Mr. Prynne, a physician who has just now returned to Boston. Following the interrogation, Hester and Prynne meet in private, where the two apologize for their respective offenses (Hester for her adultery and Prynne for his long absence, as well as for marrying such a young, vital woman—and at his age). Prynne was suspected of having been killed by Native Americans and thus was not recognized by anyone but Hester. He makes her promise not to reveal his true identity and assumes the name Roger Chillingworth.
Following her ordeal on the scaffold, Boston's officials decide to release Hester from prison. She is then allowed to build a business as a seamstress—a role in which she thrives, despite the contempt, condescension, and verbal abuse she suffers at the hands of her neighbors and patrons. Meanwhile, her daughter, Pearl, grows from an infant to a lovely, vibrant, peculiar little girl. Hester wonders at Pearl's strange mannerisms, suspecting that her daughter might be some sort of elf-child.
While delivering an order of gloves to the Governor's house, Hester speaks to the Reverend Arthur Dimmesdale, a young, sickly minister who exhorted Hester to reveal the name of the father during her interrogation on the scaffold. Later, it will be revealed that Dimmesdale himself is the father. In this scene, however, Hester is the only other person who knows this, and Pearl speaks to her father, unaware of his true identity. He, the Governor, and Chillingworth all question Hester's ability to be a good role model for Pearl. She bears these criticisms well.
Chillingworth moves in with Dimmesdale under the pretense of being the minister's doctor. In fact, Chillingworth wants to ferret out Pearl's father and has reason to suspect that Dimmesdale might be the culprit. One day, when Dimmesdale falls asleep in his chair, Chillingworth opens the minister's shirt, revealing his chest, which the Reverend has been hiding from the doctor. Though the narrator doesn't say so, the minister has been carving an A into his chest, marking himself an adulterer. The doctor sees the wound, but chooses not to treat it.
Though Dimmesdale doesn't know what Chillingworth has done (or refrained from doing), he feels a mounting discomfort around the doctor and grows to hate him. He confesses this to Hester, who's unable to reveal Chillingworth's true identity due to her oath. In the years since her public shaming, Hester's beauty has faded, the scarlet A having imposed upon her an austere life that stripped her of her great vitality. She wishes Chillingworth would exact his revenge on her instead of Dimmesdale. In effect, she wants to bear the burden of the scarlet letter alone.
Pearl fashions a green letter A out of grass. Intuitively, the girl understands that Hester wears the A for the same reason that Dimmesdale places his hand over his heart. Hester doesn't put two and two together, however, and when she and Pearl meet the Reverend on a path, her thoughts are not of his health but of Chillingworth's perfidy. Hester convinces Dimmesdale to run away with her and Pearl so that they can start over together as a family. He doesn't know how to be a father, but is so caught up in the moment that he has hope for the future.
Later, however, Dimmesdale thinks himself into believing that Hester has tempted him into sin. He rethinks their plan, which, unfortunately, cannot be put into action for four days, when the boat that will take them away from Boston departs. In the meantime, Dimmesdale's guilt drives him to climb the scaffold at night and reveal his chest, as if to tell all Boston the truth. Hester and Chillingworth, however, are the only ones who see him, and they take Dimmesdale home to rest.
The Reverend delivers a moving sermon that week, following which he reveals the scarlet letter on his chest. Without treatment, this wound has become infected. This infection has been draining the minister's health, so that when he finally admits his crime, he dies in Hester's arms. She hopes that they will meet again in Heaven and live out eternity together. In the wake of the minister's death, a purposeless Chillingworth shrivels up and dies, and Hester, heartbroken over her loss, leaves town with Pearl. Chillingworth's estate makes Pearl rich, and she never returns to Boston. Hester, on the other hand, returns years later and lives the rest of her days bearing the mark of the scarlet letter.