In Chapter X of Book the Third of A Tale of Two Cities, the reader learns that Dr. Manette was visited by the wife of one of the Evremonde twins, "a good, compassionate lady," who hoped to avert
"the wrath of Heaven from a House that had long been hateful to the suffering many."
Concerned, too, that if no atonement be made, it would one day fall upon her innocent son to do so; therefore, the Marquise Evremonde declared that she would do all that she could to make amends.
Now, fatefully, the "loadstone" beckons Charles Darnay, ne Evremonde, back to France. Having disavowed any connection to the cruelties of his family, Darnay, nevertheless, has tried to make amends by no longer taxing the peasants. And, he feels obligated to defend his former tax collector, Gabelle, who has been arrested by the bonnets rouges of the Revolution, accused of acting for an emigrant. So, Charles Darnay resolves to return to France in order to vindicate Gabelle. Another motive is Darnay's idealistic thinking that he can accomplish something positive by influencing the radicals to more reasonable actions:
Then, that glorious vision of doing good, which is so often the sanguine mirage of so many good minds, arose before him, and he even saw himself‚ in the illusion‚ with some influence to guide this raging Revolution that was running so fearfully wild.
Certainly, his sense of obligation emanates most strongly from the influence of his mother who seeks atonement for the Evremonde name.