"You have laid me under an obligation to you for life—in two senses," said his late client, taking his hand.
How lightly I valued the obligation I was conferring on my friend Mr. Charles!
"You make light of the obligation," returned Darnay, "but I will not quarrel with your light answer."
On the marriage morning, Doctor Manette had made it his one urgent and express request to Charles Darnay, that the secret of this name should be—unless he, the Doctor, dissolved the obligation—kept inviolate between them.
That night—it was the fourteenth of August—he sat up late, and wrote two fervent letters; one was to Lucie, explaining the strong obligation he was under to go to Paris, and showing her, at length, the reasons that he had, for feeling confident that he could become involved in no personal danger there; the other was to the Doctor, confiding Lucie and their dear child to his care, and dwelling on the same topics with the strongest assurances.
There are no more uses of "obligation" in the book.