In A Tale of Two Cities by Charles Dickens, Lucie Manette somehow inspires love in all the other main characters; however, the reader must accept this inspiration without understanding how it is effected since the character of Lucie is not brought to life by Dickens and remains passive.
In "Book the First," it is her golden hair that elicits the memory of his wife for Dr. Manette; and, then, the realization that he has a living daughter brings Manette back to the real world. As a hero of the Revolution, Manette is inspired to try to aid Darnay as the Revolutionaries arrest him because the son of his enemy is married to his belove daughter.
As a character, Darnay is also passive. With his tendency to get himself in trouble and be sent to jail, he is perfect for inspiring the compassion of Lucie's heart.
For Mr. Lorry, Lucie and Dr. Manette represent the family that he has never had. In his position with Tellson's Bank, Mr. Lorry assumes a protective role towards Lucie when she is but a baby. From France, he takes Lucie as an infant to England; then, he rescues her father. Mild-mannered and affectionate, he is moved by these same qualities in Lucie and feels a fatherly affection for her and grows to like and respect Dr. Manette.
Carton, as Charles Darnay's double, is equally attracted to the pretty Lucie. Seeing Darnay's and Lucie's love for each other makes Carton envious of Charles Darnay as he realizes that he could also have a happy relationship if he had not wasted his life in drink. Feeling that he cannot complete with Darnay, he remains in the background as Darnay proposes to Lucie, but he does pledge his platonic love to Lucie, promising her that he will do anything to protect her when she anxiously talks of the "echoing footsteps." He feels that if he can perform worthy deeds for Lucie and his family, he can, at least, be respected by someone. Later, of course, he makes the ultimate sacrifice for the Darnays, inspired by his love for Lucie.