The title A Tale of Two Cities is literally true as the plot involves action in both London and Paris. However, it is also significant with respect to the motif of dualities in people and in action.
Introducing the motif of dualities, the title of Charles Dickens' historical novel contains the narrative of two families during the French Revolution. There are events that occur involving these two families in both London and Paris; there are different identities of characters in each of the two cities, and there are social conditions that are similar in both of the two capital cities of England and France. In addition, subplots integrate with the main plot in intriguing ways by the end of the narrative, so, in a sense, there are more dualities.
In his opening chapter and first famous lines, Dickens writes of the similarities between England and France within the time period of the setting:
...there were a king with a large jaw and a queen with a plain face on the throne of England; there were a king with a large jaw and a queen with a fair face on the throne of France....
While the flames of revolution in France grow, Dickens notes, the burglaries and highway robberies increase the murdered count in England as the beheaded do in France. "In the midst of them [all the crimes in England], the hangman "was in constant requisition," just as in France, the men working the guillotines were in constant activity.
Charles Darnay, who meets Lucie Manette on her passage to England, is actually Charles Evremonde. He has renounced his aristocratic position and come to England as a tutor. However, he is charged with treason by a dual spy and goes on trial in London. Later, after he is called back to Paris, he again is charged with a crime against the new government and taken to prison as an oppressive aristocrat.
John Basard, whose real name is Solomon Pross, is a scoundrel who works as a double spy. He testifies against Darnay in Book I, later, he spies in St. Antoine and Paris; then in Book III he is the turnkey where Charles Evremonde/Darnay is imprisoned.
Dr. Manette, the French physician who is captured by the Evremonde brothers is falsely imprisoned in the Bastille. After the storming of the Bastille and the commencement of the Revolution in France, Manette is heralded as the prisoner who survived the aristocratic tyranny.
Dickens also employs character doubles such as Dr. Manette and Mr. Lorry, who are similar. Also, there are opposing doubles such as Madame Lafarge and Lucie Manette/Darnay. While Dickens’s doubling functions to depict oppositions, it sometimes also reveals hidden parallels. For instance, Sydney Carton seems a foil to Charles Darnay in the early part of the novel, but as the narrative progresses, he becomes an even better and more heroic person than Darnay.