Charles Darnay protects his wife Lucie not only physically but emotionally. He does not tell her his real name, but he does this to protect her from the knowledge of his family’s vicious past. He does tell her father, Dr. Manette, without knowing the role that his father and his uncle played in Dr. Manette’s imprisonment. When Dr. Manette learns the truth on the morning of Lucie and Charles’s wedding day, he reverts to his mindset of the prisoner of the Bastille.
When Charles goes to Paris to try to save his old family servant, he does not take Lucie with him, nor does he tell her where he is going before he leaves. He knows that she would want to go with him, but he wants to protect her from the possible consequences of his return to the land of his birth. When she follows him anyway, he knows what emotional turmoil she is going through, since she can do nothing to save him from the guillotine.
Even though Charles Darnay is a thoroughly good man, he protects his wife and family, not through telling the truth, but in keeping the truth from them as much as possible. He underestimates Lucie, however, who proves to be stronger than he suspected. She refuses to give up on him by returning to England without him.