It is rather fortuitous that Jerry Cruncher accompanies Sydney Carton as he goes to play his "game of cards" with Barsad and seeks to find some leverage to ensure that he can put his self-sacrificial plan into action. Barsad of course "organised" the death of Cly, which he has a certificate for. However, Jerry Cruncher, thanks to his hidden career as a "Resurrection Man" or Grave Digger, actually dug up the supposed coffin of Cly and found nothing but gravestones, which he states indignantly to Barsad:
"I tell you," said Jerry, "that you buried paving-stones and earth in that there coffin. Don't go and tell me that you buried Cly. It was a take in. Me and two more knows it."
Thus Jerry Cruncher is able to help Carton at this stage in the novel by the way that he can disprove the "death" of Cly and therefore support Carton in proving the shifting identity of Barsad, which would greatly be to his disadvantage.