In a journal form, Ezra Jennings gives the details of the experiment. He and Betteredge and Bruff work together to recreate the environment of the 18th birthday party as best they can, and placing worry about the Diamond on Franklin’s mind. Betteredge and Bruff are at first skeptical and uncertain about Ezra Jennings’s experiment, but they cooperate. Ezra Jennings writes to Rachel in secret, so she can be present when they try the experiment. He explains the high possibility of Franklin acting under influence of the drug; this convinces her, largely, of his innocence. They continue to make preparations so that Franklin is in his original restless, sleep-deprived state without his cigars. Finally, Rachel and Ms. Merridew and Mr. Bruff arrive (Rachel and her guardian in secret). The night of the experiment, Franklin finally falls asleep, but soon begins mumbling about how the Diamond was not safe in the house, and how he should have left it in the bank. He sits up, and deliriously walks to Rachel’s cabinet and removes the fake Diamond, ready to take it to the bank in the morning. However, since he was given a slightly higher dose, he collapses and falls asleep before leaving Rachel’s sitting room.
Now that everyone else is convinced of Ezra Jennings’s theory, Bruff contemplates the Diamond’s current location, since it is almost certainly in the London bank, pledged by Luker. Rachel happily watches over the sleeping Franklin; Ezra Jennings is grateful to be happy for one last time before his impending death.
This fourth narrative consists of extracts taken directly from Ezra Jennings. It is assumed that these are extracts picked out by Franklin (and Mr. Bruff) after Ezra Jennings’s death. Ezra Jennings shows himself to be a sensitive character, noting particularly the relationships between people and way people treat him. He notes Betteredge’s skeptical tone when it comes to trusting Ezra Jennings, as well as the old man’s religious preoccupation with Robinson Crusoe. He is particularly sensitive about Franklin and Rachel’s love for each other, and fond of both of them; they likely remind him of his own failed love.
Ezra Jennings also describes the horrible nightmares he has when taking opium, yet he continues to take the drug because of the terrible pain he experiences if he doesn’t. This is likely taken from Collins’s own experiences and addiction to it.