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.
Franklin awakes in the morning to lay eyes first on Rachel. Jennings leaves them alone. Franklin and Rachel are happily reconciled and thank Jennings for his efforts. Everyone but Jennings leaves for London.
Ezra Jennings's journal, which we later discover was willed to Franklin by Jennings upon his death, presents us not only with a report of the preparations of the experiment but also of a picture of an opium addict. The genre was somewhat common—Jennings himself recommended Thomas de Quincy's Confessions of an Opium Eater to Franklin. Jennings's diary presents himself as a man torn between the pain of his disease and the frightfulness of his opium addiction (Jennings is taking a dosage more than ten times the size of the dose he gives to Franklin). Passages describing his opium dreams are supposed to be direct experiences of Collins's, when he himself was taking opium.
Jennings's status as Franklin's outcast double is reinforced in these extracts from his diary. Jennings's former love is alluded to in his writing ("the one beloved face which I shall never see again"), and this sets him up as part of a tragic, unfulfilled counterpart to the reconciled couple, Franklin and Rachel. Jennings is accordingly happy to render Franklin and Rachel the service of enabling their reconciliation, living vicariously through the happiness of their union.
Franklin and Jennings are further aligned in their knowing, "outsider" versions on typical solid English character traits. Jennings amuses himself thinking of the skepticism and "wonderful sameness" of the English character as seen in Mrs. Merridew, Mr. Bruff, and Betteredge. Jennings makes the English character seem unimaginative and stubbornly backward. He remarks upon the protest "against anything that is new," notes Mr. Bruff's "unimaginative mind," and jokes about the particular ability that traditional English literature has in "enchaining nobody's interest, and exciting nobody's brain." These comments recall the fact that Franklin has an exciting amount of Italian, German, and French in him and that he has himself lamented the unimaginative nature of the English mind by implication: in Chapter VI of Betteredge's narrative, Franklin states, "But then I am an imaginative man; and the butcher, the baker, and the tax-gatherer, are not the only credible realities in existence to my mind."
Much of Jennings's journal is concerned with preparations to make the night of the experiment as similar to the night of Rachel's birthday as possible. Of course, an exact repetition of a past moment is impossible, and Betteredge's protests that buzzard and a cupid will be missing from the Verinder home, are a parody of this protest. Jennings's narrative, however, is clearly aware that an exact repetition is impossible—Jennings stresses that the reenactment is an "experiment" and that the conditions of Rachel's last birthday will only be approximated, not replicated. Thus, when Franklin passes out after taking the diamond, but before demonstrating what he did with the diamond the night of the theft, the experiment is still a success.