Dimmesdale is part of the group of ministers sitting in judgment over Hester when she emerges from prison. But he exhorts her to reveal the name of the man who was her lover. He suggests that it might be better for that man, too, if he were revealed.
Dimmesdale slowly begin to change. He holds his hand over his heart as if something there hurts him. He seem to be ailing.
Dimmesdale and Dr. Chillingworth strike up a friendship. Dr. Chillingworth moves in with Dimmesdale and becomes his personal physician.
One night, wandering around, Dimmesdale happens to run into Hester and Pearl. He sees Chillingworth and does not recognize the man – Chillingworth looks like an evil apparition to Dimmesdale.
Dimmesdale looks at the sky and sees a large scarlet letter – the letter A – marked out in dull red light in the sky. It is further proof of his guilt, in his mind.
One night, Chillingworth observes Dimmesdale asleep. He undoes Dimmesdale’s shirt and grins at what he sees there.
Hester and Dimmesdale decide to run away together. This opens Dimmesdale up to his bad side: he wants to do all sorts of things he has never wanted to do before.
He has to exert extreme self-control over his tongue to keep himself from destroying other people’s faith and lives.
On Election Sunday, he preaches his last sermon, proceeds to the scaffolding and, with Pearl holding his hand as a physical connection to Hester, makes a confession to his congregation and to the citizens of Boston.
Opening his clothing, he reveals the scarlet mark on his chest, over his heart—the mark of his sin, a letter A.
With this, Dimmesdale dies, but not before telling Hester that this is the mercy of God—that God would not let him die an unrepentant sinner but has been after him for seven years to confess.