Sydney Carton decides to make sure he is seen around Paris. He eventually wanders into a wine shop—Defarge's wine shop. Defarge and Madame Defarge marvel at his physical resemblance to Charles, but have no idea who he is.
Carton wants to make sure that it is known that there is someone who looks just like Darnay walking free on the streets of Paris.
Carton eavesdrops on a conversation between Defarge, Madame Defarge, The Vengeance, and Jacques Three, in which Madame Defarge plots to exterminate the Evrémonde line—including Lucie and Lucie's daughter. She says that she and the wood-sawyer will testify against Lucie for sympathizing with a prisoner. Jacques Three promises a conviction. Monsieur Defarge, however, hesitates, and suggests that poor Dr. Manette has suffered enough.
The bloodthirsty juries of the Revolution need only the slightest suspicion to convict someone. Jacques Three's promise indicates that there is no justice, and that the trials are shams. Monsieur Defarge's pity for Manette makes Madame Defarge's utter mercilessness stand out even more starkly.
Madame Defarge responds by revealing her history with the Evrémondes: she is the missing sister of the peasant family whom the Evrémonde brothers abused and killed. She vows to carry out her brother's dying curse. She barks at Defarge that he can tell wind and fire where to stop, "but don't tell me." Jacques Three and The Vengeance are thrilled.
Madame Defarge exceeds the forces of nature. She is a the terrifying product of tyrannous cruelty. She symbolizes all of the people abused by the aristocrats, and her vengeance is the embodiment of the Revolution.
Carton hurries home. Soon, Dr. Manette returns too, begging for his shoemaker's bench. Shocked, Carton and Mr. Lorry realize that Dr. Manette has lost his mind. Carton instructs Mr. Lorry to gather everyone's passports, including Carton's, and leave the next day before Madame Defarge's accusations make it impossible for them to leave France. Then Carton says farewell, blesses Lucie, and leaves.
A key tipping point: the curse against Charles cannot be stopped, and Dr. Manette's insanity is now permanent. After failing to save Charles, Manette reverts to his own fate as a traumatized prisoner. Carton takes control of things, setting up his final plan.