In Book Three, Chapter Ten of A Tale of Two Cities, “The Substance of the Shadow,” Alexandre Manette takes over as the story’s narrator. His letter is a flashback that reveals the circumstances leading to his imprisonment in the Bastille.
Dr. Manette is summoned to a country house late at night where he meets the aristocratic Evrémonde brothers. They lead him to a room where a young woman, apparently suffering from a fever, is tied to a bed. After Manette treats her, the brothers lead him to a second patient, a young man who has been stabbed by a sword. The young man explains that the girl is his sister and that the two noblemen raped her, then attacked him when he tried to defend her. When Manette attempts to contact the authorities on the brother and sister’s behalf, the Marquis St. Evrémonde has him thrown in prison.
This flashback provides an unexpected window into Manette’s mind, which has previously been closed to readers, other characters, and at times, even Manette himself. It also reveals the reason Manette did not want to hear Darnay’s real name—he likely suspected that Darnay was actually an Evrémonde.
Manette’s story is also a metaphor for the prevailing political situation in pre-Revolutionary France. The nobility is able to exploit the peasants with impunity since they have influence with the justice system.