Franklin leaves a note for Betteredge telling him that he's going to be late for dinner.
In Mr. Candy's office (which is filled with skeletons and medical books), Jennings gives Franklin a few handwritten manuscripts.
Before Franklin looks at them, Jennings asks him if he remembers any conversation during dinner, the night of the birthday party, about the medical profession.
Franklin remembers having argued with Mr. Candy about whether or not certain medicines were effective.
Jennings isn't surprised – he's almost positive that Mr. Candy gave him opium in order to prove a point.
The first manuscript that Jennings gives to Franklin is a word-for-word transcript of what Mr. Candy said during his fever.
It's a bunch of disjointed words and phrases, and although Franklin's name comes up several times, he can't make heads or tails of it.
But the second manuscript fills in the gaps: Jennings has gone through it and filled in missing words and phrases, based on what he thought was probably, to make the ideas coherent.
Basically, the second manuscript is a confession by Mr. Candy of having slipped some opium into Franklin's bedtime brandy (with help from Godfrey Ablewhite) in order to prove that opium could help him sleep better.
Of course, the manuscript is useless as a legal document – it wouldn't hold up in court.
But Franklin is now convinced that this must be how he stole the Moonstone without being aware of it.
The question is, what happened to the diamond afterward?
After all, the diamond ended up being taken to London, and he can't use opium as an excuse for that.
Jennings proposes that they try an experiment: Franklin should give up smoking cold turkey again, just like he did the previous June.
Then he should try to replicate as closely as possible the events of the evening of the birthday party, try taking some opium, and see what happens.
Maybe he'll go through the same motions again while he's in his opium trance, and they'll be able to watch him to see what he does.
And maybe, just maybe, they'll be able to figure out what he did with the diamond after he took it.
Franklin agrees to try it, and suggests that they invite Mr. Bruff to come as a witness.
Jennings also offers to write to Rachel to tell her everything that they've discovered, and to tell her about the proposed experiment and ask her permission (since, after all, it would take place in her house).