Charles Darnay’s secret is that his real name is Charles St. Evremonde and he is the heir to the title of Marquis St. Evremonde, the man who put Dr. Manette in prison.
Charles Darnay did not want to tell the Manettes his real name. He was ashamed of being a St. Evremonde. He did not approve of his uncle’s treatment of the peasants. Therefore, Charles wanted to renounce his title.
Charles seeks a private talk with Dr. Manette. He wants to tell him that he loves Lucie. It is important to Charles that Dr. Manette knows his real name.
“I wish it, that I may the better deserve your confidence, and have no secret from you.” (2:10)
Dr. Manette bristles. He does not want to know Charles’s real name. Charles tells him he has changed his name, and he is not from England. The doctor yells at him to stop every time he tries to say it. He allows Charles to tell him on the morning of their marriage.
Dr. Manette understands how the news will affect him. Anything having to do with his imprisonment sends him into shoe-making relapse. He knows that this will happen if Darnay tells him anything about his past. He asks Charles to wait, because then the young couple will go away on their honeymoon and not know what happens to Dr. Manette. He wants Lucie to be in the dark about everything, so her wedding is not ruined and she does not worry about him.
The fact that Charles needed to tell Dr. Manette who he was so badly is a sign of his character. He does not want to feel like he is marrying Lucie under false pretenses. He loves Lucie, but he does not want Dr. Manette to ever think he lied. Marrying the daughter of one of his father’s victims is not an easy thing for him, but he is trying to escape his past.
Dr. Manette likewise tries to avoid hurting Lucie. At first, he does not want to hear the news. Yet he understands how important it is to Charles. In one of the major themes of the book, he makes a sacrifice to hear the news, knowing he will relapse. He recovers fairly quickly, showing his recovery is progressing.