In this chapter, we learn that in the late nineteenth century, Mr. Manette was poisoned with thallium, a chemical used in the production of electric currents. Although the police were unable to find any evidence of the cause of his illness, his workplace was near a research laboratory. Because of the proximity of the laboratory, everyone was forced to treat the incident as an accident, and the complications from the poisoning were irreversible. The narrator tells us that it has been many years since he has spoken to anyone about his father's strange behavior. He says that his father has turned into a "little baby," and that he feels better after getting rid of all traces of the chemical.