This section consists of extracts from Ezra Jennings's journal. Throughout the extracts, Jennings writes of the pain of his disease and the horrible dreams brought on by his opium use.

On June 15, Jennings completes his letter to Rachel asking her assistance with the recreation of the crime. On June 16, Jennings checks on Franklin. Jennings wonders why he feels attracted to Franklin—perhaps because of Franklin's openness and trust. On June 17, Rachel writes back to Jennings thanking him and stating her belief in Franklin's innocence. Jennings keeps Rachel's change of mind a secret from Franklin. She wants to meet with Franklin before the experiment and vindicate him, but Jennings asks her to come secretly on the night of the re-enactment so as not to disturb the experiment.

On June 18, Jennings meets with Betteredge and Franklin. Franklin reports that Mr. Bruff is suspicious of Jennings and unsupportive of the experiment. Betteredge is suspicious as well but obeys the orders of Rachel to cooperate. Betteredge and Jennings review the preparations to put the house back in order as it was last year. Betteredge is stubborn, pointing out details that cannot be replicated.

On June 19, Mrs. Merridew writes to Jennings announcing her intention to chaperone Rachel to the experiment. On June 20, Franklin reports receiving a reply from Sergeant Cuff, and Jennings urges him to invite Cuff to be present for the experiment. Betteredge shows Jennings a passage in Robinson Crusoe, which seems to prophetically confirm Betteredge's own doubts about the experiment, but Jennings ignores the passage as a mere coincidence. On June 21, Franklin reports that he continues to sleep poorly without his tobacco. On Friday, June 22, the men set the date for the experiment as Monday, June 25.

On June 25, Franklin, Jennings, and Betteredge do their best to recreate Franklin's actions on the night of Rachel's birthday. Jennings puts Franklin in his bedroom at nine o'clock. At ten o'clock, Mr. Bruff, Rachel, and Mrs. Merridew arrive. Jennings meets with Rachel, who is momentarily taken aback by his appearance, but who then expresses her gratefulness to him. Rachel notices the suspiciousness of the household staff toward Jennings and asks him about it. Jennings replies that it is "only the protest of the world … on a very small scale against anything that is new."

At eleven o'clock Jennings administered the laudanum to Franklin, witnessed by Mr. Bruff and Betteredge. Jennings encourages Franklin to discuss the subject of the Moonstone, and the dangers surrounding it. The opium begins to take effect after midnight, and Franklin sits up in bed and talks to himself about his doubts about the diamond's and Rachel's safety. He soon arises and goes to Rachel's room, repeating his actions on the night of the theft. After he takes the diamond in his hand, however, the sedation overcomes him, and he sits on Rachel's couch and sleeps. Mr. Bruff, Betteredge, and Rachel are now convinced of Franklin's innocence, yet the mystery still remains as to the current whereabouts of the diamond. Mr. Bruff proposes to leave for London in the morning to resume his watch on Mr. Luker's bank.