In Book 2, Chapter 2, Charles Darnay is on trial at the Old Bailey. He is accused of treason, or, as the court said:
he was a false traitor to our serene, illustrious, excellent, and so forth, prince, our Lord the King, by reason of his having, on divers occasions, and by divers means and ways, assisted Lewis, the French King, in his wars...by coming and going between dominions...and those of the said French Lewis, and...revealing to the said French Lewis what forces our said serene, illustrious, excellent, and so forth, had in preparation to send to Canada and North America.
In other words, in the midst of the American Revolution, Darnay was accused of having informed the French, who had intervened militarily in the conflict, about the number of troops the British were sending to fight. This constituted treason, or conspiring against the king, an offense that carried the dreadful punishment of being hanged, drawn, and quartered.
The man who is on trial for treason is Charles Darnay.
Silence in the court! Charles Darnay had yesterday pleaded Not Guilty to an indictment denouncing him (with infinite jingle and jangle) for that he was a false traitor to our serene, illustrious, excellent, and so forth, prince, our Lord the King,
This chapter is told from the perspective of Mr. Jerry Cruncher, who often performed odd jobs for Mr. Lorry. On going to deliver a message to Mr. Lorry, he witnesses the courtroom scene where poor Charles is on trial for treason against the king of England. His largest infraction seems to be that he is French, and Jerry notes that the prisoner looked like a gentleman, "well grown and well looking."
The chapter concludes with the crowd murmuring about the possible witnesses on the bench, a young lady and her white-haired father; of course, these are Lucie and Dr. Manette.