In Chapter XXIV of Book the Second of A Tale of Two Cities, Darnay is in Tellson's Bank, speaking with Mr. Lorry, who prepares to go to Paris.  There the Revolution finds the culottes-rouges seizing the property of the aristocrats.  Since the Marquis Evremonde has been murdered, the court that is trying the aristocracy has seized Gabelle, the tax collector for the Evremondes. Now, Gabelle has sent an urgent message to Tellson's Bank, knowing that many an emigrant of title has kept his money in this bank.  In this letter, he explains that he has told the tribunal that he gathered nothing from those who are supposed to pay taxes. And, he pleads with Charles Evremonde,

For the love of Heaven, of justice, of generosity, of the honour of your noble name, I supplicate you, Monsieur heretofore the Marquis, to succour and release me. My fault is, that I have been true to you. Oh‚ Monsieur heretofore the Marquis, I pray you be you true to me!

It is this plea that is the catalyst for Darnay's fateful return to France.  For, he feels compelled to return to his homeland and plea for the lifie of Gabelle despite the terrible risk to his personality.