Hester decides to ask Chillingworth to stop tormenting Dimmesdale. When she and Pearl encounter him on a beach near the sea, he tells her the council has recently discussed allowing her to remove the scarlet letter from her chest. She says the letter should stay until she's worthy of its removal.
Hester will remove the letter only on her own terms. Her remark about being worthy of its removal is a sarcastic jab at the Puritans, who seek to define her worthiness.
Hester notices that Chillingworth has changed. He's now a wretched, vengeful old man. Chillingworth also notes the change, remembering when he was a kind scholar. He says that he's lost his "human heart."
Chillingworth's secrets and his quest for revenge have made him inhuman, unable to forgive, and miserable.
Hester tells Chillingworth he holds Dimmesdale's life in his hands. Chillingworth says he saved Dimmesdale's life by not revealing his link to Hester from the start. Hester says he would be better off dead than forced to endure Chillingworth's torture.
Chillingworth, and other Puritans, equates reputation with life. But Hester knows prioritizing reputation over the soul is killing Dimmesdale.
Chillingworth admits that he's become a "fiend." He blames Hester for his downfall. Hester agrees, pleading with Chillingworth therefore not to blame and abuse Dimmesdale any further.
Unlike anyone else in the novel, Hester is "true." She admits her mistakes and sins and takes responsibility for them.
Hester says she must tell Dimmesdale about Chillingworth. He responds that their fate, a "black flower," is no longer in anyone's hands. He apologizes to Hester for not having offered her the love that would have prevented their collective ruin.
Prisons are black flowers because they arise out of sin, which they're intended to contain. Similarly, Chillingworth intended to punish sin, but has instead become sinful himself.