In Book the Third, Chapter 1, Charles Darnay is referred to by the officer in Paris as a "prisoner".  Darnay is shocked by this "disagreeable word", and reminds the officer that he is "a free traveller and French citizen, in charge of an escort which the disturbed state of the country had imposed upon him, and which he had paid for".

Darnay has inadvisedly returned to France to secure the release of Gabelle, who has been arrested while in his service.  Darnay has no idea of the extent to which conditions have deteriorated in France, and is caught up in the middle of a violent revolution.  On his journey from London to Paris, Darnay is stopped multiple times by various groups questioning his identity.  He is derided for being an emigrant and an aristocrat, and learns that a decree has, or will soon be passed, "banishing all emigrants and condemning all to death who return".

Finding himself at the mercy of the "capricious judgment...(of) the dawning Republic", Darnay realizes that "there (is) no hope of return until he should have been declared a good citizen at Paris".  Bowing to the demands of "patriots", he pays to be escorted to the city, where, to his chagrin, he is greeted as a "prisoner".  When Darnay demands "under what law, and for what offence" he is being held, he is told unceremoniously that there are "new laws" and "new offences" in France since he has been there last.  He is told flatly that, as an emigrant, he has "no rights", and is remanded to prison "in secret".