In Chapters 4 and 6 Dr. Manette has a strong and rather peculiar reaction to a particular person. Who is this person and what is Dr. Manette’s reaction? At what does this hint? (Book 2 Chapters 1-6)

I'm not exactly sure which character you are referring to but you might consider. Mr. Darnay. After dinner (chapter 6), Mr. Darnay comes to call. Dr. Manette is in good humor until he gets flustered when Darnay tells a story about the Tower of London, in which many prisoners' initials were carved. The only ones that couldn't be matched by a former prisoner were D.I.G., which the guards figured was an imperative to dig (they dug, but found only remains of a possible letter).