Who is the third person who denounces Darnay? What are the circumstances of the denunciation? (From Book 3 Chapters 6-10)

The tribunal names the three who denounced him and they include Monsieur and Madame Defarge and, surprisingly, Doctor Manette. He protests that this is impossible, but Monsieur Defarge produces the document from Doctor Manette's cell in the Bastille.

Dr. Manette's document, written in his cell in the Bastille and hidden in its chimney in 1767, explains why he was imprisoned. When he was a young and successful doctor, he was accosted in the street by what he perceived to be a pair of twins. They asked him to enter the carriage and showed him that they were armed. They refused to give him details about the patient.

In the narrative of the document, Manette enters the carriage and they drive him to a solitary house, where he hears the cries of a woman. She is a beautiful young woman, whose surname Dr. Manette never learns, tied up on a bed, and she is raving with brain fever. She repeats the phrase "my husband, my father, and my brother!" and counts to twelve obsessively. The other patient in the house is a young peasant, her brother, who is dying of a knife wound. He explains that the noblemen had tried to exercise their feudal "right" to have sex with their serfs, but his sister was a virtuous girl and would not let them. The lord then tied her husband to a cart like a horse and drove him to death. He died in his wife's (the first patient's) arms, sobbing once every stroke of the clock at noon, explaining her fixation on the number twelve. He then took the girl to rape her. The boy took his other sister to a safe place and then attacked the noblemen, who gave him the fatal stab wound. As he dies, the boy curses the nobleman and his family.

The doctor is disturbed by this story and even more worried when he sees that the girl has recently become pregnant. The noblemen ask him to keep everything he has seen and heard a secret, but they grow alarmed when he refuses to accept their payment for his medical services. The girl dies, and the noblemen seem unconcerned. The doctor is returned to his lodgings. Knowing full well that any letter he writes will be ineffective because of noble influence on the court, he finishes a letter to the Minister, and the wife of the Marquis St. EvrÃmonde calls on him, clarifying the mystery of the nobleman's last name. She is the wife of the man who raped the peasant and wants to do penance by finding her living sister and doing well by her, but she doesn't know where to find her. Neither does Dr. Manette, so the Marquess leaves with her son, Charles Darnay, musing that he will eventually have to pay for the sins of the family if she cannot expiate them herself. The same night, a man demands to see Dr. Manette, captures him, and the two brothers burn the protesting letter that he had written in front of his face. He is thrown in the Bastille on their authority, and Dr. Manette denounces them and their family members.