I call it the detective-fever; and I first caught it in the company of Sergeant Cuff
For some reason this little section is so funny to me. It almost reads like a Buddy Comedy or something. I also think that it's sort of supposed to feel like a bit like things are starting to come full circle as we get near to the end of the story. The same setting is back, the same jokes are back, we're back with Betteredge and encouraged to feel comforted by that through Franklin's narrative.