The darkness motif with its images of shadows in A Tale of Two Cities points to the inscrutable quality of human nature along with a sense of foreboding and mystery and often gloom. In Chapter 3 of Book the First, for instance, Dickens digresses from his narrative to reflect upon the fact that "every human creature is constituted to be that profound secret and mystery to every other." Certainly, many of Dickens's characters are, indeed, do have a darker side to them:
- Jerry Cruncher is a "resurrection man" at night
- Mr. Lorry is lost in the dark confines of Tellson's bank where he is figuratively buried from others. Once he becomes involved with the Manette family he is happier for a time; however, the worries of Mr. Lorry for his friends in France increase, especially when Dr. Manette's letter implicates Charles Darnay. In Chapter 18 of Book the Second, Mr. Lorry's concern for Manette increases, his "hope darknened and his heart grew heavier."
With a hope ever darkening, and with a heart always growing heavier and heavier, Mr. Lorry passed through this anxious time.
- Dr. Manette has a dark part of his life that "casts a shadow beyond" himself that falls upon his son-in-law. In Chapter 10 of Book the Third, "The Substance of a Shadow" is revealed and implicates Charles Darnay as the son of one of the dastardly Evremonde twins who have Manette imprisoned. After his letter is read to the revolutionaries, "a shadow" falls over Manette and he seems lost again as in his dark days of imprisonment.
- Charles Darnay has a dark past inherited from his father that he seeks to escape by coming to England after changing his name.
- Madame Defarge certainly has a dark secret in her heart with which she harbors her plan of vengeance. In Chapter 5 of Book the Third, as Lucie stands in the fresh white snow, Madame Defarge passes by "like a shadow over the white road" and she includes Lucie and her child in the deadly plan. In Chapter 3 entitled "The Shadow," in Book the Third, Madame Defarge knits Lucie and her child into the register of death:
- Later in the Chapter entitled "Darkness," Chapter 12 of Book the Third, Madame Defarge's dark plan to have Darnay executed is revealed.
- Solomon Pross, beloved brother of Miss Pross, lives a dark life of espionage and treachery.
- Sydney Carton, ironically, presents his darker side to the world, and it is his more noble side that finally emerges in his self-sacrifice for the love of Lucie Manette.
Shadows continually fall throughout A Tale of Two Cities, creating a sense of mystery, foreboding, obscurity, and gloom.