Dickens uses Doctor Manette to illustrate one of the dominant motifs of the novel: the essential mystery that surrounds every human being. As Jarvis Lorry makes his way toward France to recover Manette, the narrator reflects that “every human creature is constituted to be that profound secret and mystery to every other.” For much of the novel, the cause of Manette’s incarceration remains a mystery both to the other characters and to the reader. Even when the story concerning the evil Marquis Evrémonde comes to light, the conditions of Manette’s imprisonment remain hidden. Though the reader never learns exactly how Manette suffered, his relapses into trembling sessions of shoemaking evidence the depth of his misery.

Like Carton, Manette undergoes a drastic change over the course of the novel. He is transformed from an insensate prisoner who mindlessly cobbles shoes into a man of distinction. The contemporary reader tends to understand human individuals not as fixed entities but rather as impressionable and reactive beings, affected and influenced by their surroundings and by the people with whom they interact. In Dickens’s age, however, this notion was rather revolutionary. Manette’s transformation testifies to the tremendous impact of relationships and experience on life. The strength that he displays while dedicating himself to rescuing Darnay seems to confirm the lesson that Carton learns by the end of the novel—that not only does one’s treatment of others play an important role in others’ personal development, but also that the very worth of one’s life is determined by its impact on the lives of others.