The Scarlet Letter begins with a prelude in which an unnamed narrator explains the novel's origin. While working at the Salem Custom House (a tax collection agency), the narrator discovered in the attic a manuscript accompanied by a beautiful scarlet letter "A." After the narrator lost his job, he decided to develop the story told in the manuscript into a novel. The Scarlet Letter is that novel.
The novel is set in seventeenth-century Boston, a city governed by strict Puritan law. The story begins as Hester Prynne, the novel's protagonist, is led out of a prison carrying an infant, named Pearl, in her arms. A bright red "A" is embroidered on her chest. A crowd waits expectantly as Hester is forced to climb up a scaffold to endure public shame for her sin. While on the scaffold, Hester is terrified to recognize her estranged husband, Chillingworth, in the crowd. He recognizes her too, and is shocked. Chillingworth pretends not to know Hester, and learns her story from a man in the crowd: she was married to an English scholar who was supposed to follow her to Boston but never showed up. After two years she fell into sin, committing the adultery that resulted in her baby and the scarlet "A" on her breast. Chillingworth predicts the unknown man will be found out, but when the beloved local Reverend Arthur Dimmesdale commands Hester to reveal the man's name, she refuses and is sent back to her prison cell. Chillingworth poses as a doctor to get inside the prison to speak with Hester, and there forces her to promise never to reveal that he's her husband.
Three years pass. Hester is let out of prison and moves to the outskirts of Boston, near the forest. She makes a living as a seamstress, though the people who employ her still shun her. Hester refuses to tell Pearl what the scarlet letter signifies, and Pearl becomes obsessed with the letter. Meanwhile, Chillingworth is working in Boston as a physician, though he has no formal medical training. One of his patients is Dimmesdale, who has fallen ill with heart trouble. Chillingworth moves in with Dimmesdale to care for him full-time and begins to suspect a connection between Dimmesdale's heart ailment and Hester's crime. When he discovers that Dimmesdale has carved a mark over his heart that resembles Hester's scarlet letter, Chillingworth realizes that Dimmesdale is Hester's lover. Chillingworth decides to torment and expose Dimmesdale.
Under Chillingworth's cruel care, Dimmesdale's health deteriorates. Dimmesdale's guilt for committing and concealing adultery causes him profound emotional suffering. He even starves and whips himself as punishment. One night Dimmesdale mounts the same scaffold upon which Hester was publicly shamed. At just that moment, Hester and Pearl pass by and join Dimmesdale on the scaffold. A meteor lights the sky in the shape of a red "A" and illuminates Chillingworth standing nearby.
Hester decides she must help Dimmesdale, and pleads with Chillingworth to stop tormenting him. Chillingworth acknowledges that he's become cruel and wicked, but argues that he's actually protecting Dimmesdale by not revealing his secret to the public. Hester then takes matters into her own hands: she intercepts Dimmesdale in the forest and tells him Chillingworth's true identity. She convinces Dimmesdale to flee with her and Pearl to Europe, and they make plans to take a ship the day after Dimmesdale is scheduled to deliver an important sermon. Dimmesdale delivers the sermon (the best of his life). However, he realizes he's dying and won't make it to Europe. He mounts the scaffold and asks Hester and Pearl to join him. He confesses his sin to the crowd and bares his chest, revealing a scarlet letter carved into his own skin. He dies as Pearl kisses him for the first time.
Hester and Pearl leave Boston. Chillingworth dies a year after Dimmesdale, leaving Pearl a small fortune as an inheritance. Many years later, Hester returns to her cabin on the outskirts of town. She still wears her letter "A." Pearl has married into money in Europe and writes to Hester on occasion. Hester remains in Boston until her death and is buried alongside Dimmesdale. Their shared tombstone bears a letter "A."