What is Jerry Cruncher's secret nighttime activity, and what important theme does this activity underscore in A Tale of Two Cities?
Jerry Cruncher's euphemistically-termed occupation as "resurrection man" proves pivotal to the plot of A Tale of Two Cities while he is still in England as he observes the funeral of Roger Cly. For, later, after the funeral, Jerry decides to rob the grave and discovers that the coffin is filled with dirt and rocks.
Related to the theme of resurrection, in Chapter 8, "A Hand at Cards," of Book the Third of the novel, in a fantastic coincidence, Jerry and Miss Pross are shopping for groceries and run into her brother Solomon, who is, in fact John Basard, the spy and the "Sheep of the prison." Then, another coincidence occurs as Sydney Carton and Mr. Lorry appear on the scene. Carton looks at Basard/Solomon and recognizes in Basard--"I know the face"--the man who testified against Charles Darnay at the treason trial for the French aristocrat. But, this Roger Cly, whom Basard claims the witness was, Carton observes, spoke "good French. Yet like a foreigner." He then says,
"Cly! Disguised, but the same man. We had that man before us at the Old Bailey."
Now Carton has "cards" to play against Basard, the jailor at the prison. But, Basard contends that Cly, who was his partner, has been buried in London. It is here that Jerry interjects his knowledge that Cly was never truly buried, revealing that the coffin was empty. This gives Carton the edge that he needs, the cards to play, to control John Basard. Thus, he is able to have Basard, who fears his exposure to the revolutionaries, let him into Darnay's cell so that he can switch places, resurrecting Darnay from prison as his father-in-law was also resurrected, and thereby providing Carton a spiritual resurrection as he becomes the sacrificial victim for Charles Darnay.
Jerry Cruncher, at night, is a "resurrection" man, which is a polite term for grave robber. At that time, doctors could not study human physiology legally. They had to pay men who would dig up the corpse so that the doctors could learn more about anatomy and physiology. No one donated their body to science back then.
A major theme of the novel is death and resurrection. Jerry's "work" dealt with the dead whom he "resurrected" to teach doctors more about how to treat their patients with a better rate of success. The dead's resurrection led to patients being given the gift of life at the hands of a more knowledgeable doctor.