Mr. Bruff and Franklin meet back at Franklin's house and discuss further ways of investigating the diamond theft. Mr. Bruff suggests that they set a guard outside Mr. Luker's bank toward the end of the month and see who redeems the diamond. Franklin cannot wait that long and sets off at once to try to get Sergeant Cuff out of retirement. Arriving at Cuff's house, Franklin finds that he is visiting Ireland. Franklin leaves a card for him and returns to London.
Franklin next visits Mr. Bruff and announces his resolve to question all guests at the birthday dinner, beginning with the guests currently living in London. Mr. Bruff informs him that Miss Clack has moved to France, that Mr. Murthwaite is on his way to another Eastern adventure, but that Godfrey may be in London. A man at Godfrey's club gives Franklin several pieces of information about Godfrey: since his broken engagement to Rachel, Godfrey had become engaged to another heiress. This engagement had also been broken off due to a dispute over "settlements." Godfrey had then inherited 5,000 pounds from a rich, old, charity lady upon her death, and had used the money to travel to Europe.
Franklin next resolves to return to Frizinghall and question Betteredge about the other guests. Arriving at his hotel in Frizinghall, Franklin remembers hearing that Mr. Candy, who lives around the corner, wanted to speak to him and was also a guest at the birthday dinner.
Franklin goes to Mr. Candy's and finds the doctor much changed. Mr. Candy is a "wreck," dressed gaudily and unable to complete any thoughts. Candy seems to have something important to tell Franklin regarding the night of the birthday dinner, but he is unable to remember. Franklin gives up. On his way out, Ezra Jennings approaches him.
Ezra Jennings and Franklin begin to walk outside together. Franklin is intrigued by Jennings's strange appearance and feels sorry for him. Franklin is impressed that Jennings carries himself like a gentleman. Jennings explains that he was born of mixed parentage and raised outside of England in a colony.
Jennings broaches the subject of Mr. Candy's illness. He explains that Candy fell ill riding home in the rain from Rachel's party. Contrary to other doctors' orders to put him on depressants, Jennings put him on a steady diet of stimulants—champagne and brandy—until his pulse steadied. Jennings explains how he cried with "hysterical relief" when Candy began to improve—Jennings has a "female constitution." When Candy came to, he couldn't think or speak in complete thoughts. Jennings began to write down his mumblings in shorthand, filling in the gaps later to make sense of them.
Jennings informs Franklin that one of the mumblings spoke of him, but Jennings cannot show the private document to him unless he is convinced of Franklin's interest in the content. Franklin, ashamed, gives a bland explanation about the investigation of the diamond. Jennings informs him that Candy's mumblings didn't concern the diamond and walks away.
Franklin stops Jennings and explains there is more to his own interest than he is revealing. Jennings apologizes for embarrassing Franklin and sits down in the woods to tell Franklin his own circumstances. Jennings, some years back, was accused of a horrible crime that he did not commit, but he cannot prove his innocence. Candy employed him in spite of this questionable background. The slander will soon follow Jennings to Frizinghall, but by that time Jennings will be dead—he suffers from a terminal illness and is kept alive now only by his copious use of opium as a pain-killer.
Franklin now explains to Jennings his part in the diamond theft. Jennings becomes excited and asks Franklin if he has ever used opium—Franklin hasn't. Jennings asks Franklin if he remembers sleeping soundly for the first night in a while the night of the theft—Franklin does. Jennings tells Franklin that he can prove that Franklin was unconscious of his actions that night. Franklin agrees to meet Jennings at Mr. Candy's in two hours to hear the explanation.
Franklin arrives back at Mr. Candy's to meet with Jennings. Jennings questions Franklin and is satisfied by the answers: Franklin had had difficulty sleeping on the nights before the theft because of his giving up of smoking; Franklin had had a dispute with Mr. Candy during dinner about the profession of medicine; Franklin had felt extreme anxiety about the Moonstone the day of Rachel's birthday. Jennings produces a transcript of Candy's mumblings and another transcript of the mumblings expanded to make sense. They reveal that Candy gave Franklin a dose of opium without Franklin's knowledge to prove to him that medicinal prescriptions are effective and not, as Franklin had said, "gropings in the dark." Under the influence of this drug, Franklin had retrieved the diamond during the night, in response to his worry to keep it and Rachel safe.
Franklin and Jennings are convinced of Franklin's innocence—now they must prove it to others. Jennings proposes that Franklin quit smoking again now, and that they recreate the night of the theft, putting Franklin under a dose of opium again and watching his actions. Jennings produces various medical books that testify that a man's actions, even when performed under the influence of drugs, are etched on the memory and can be recreated when back on the drug. Jennings offers to write to Rachel requesting permission to set up the Verinder house as it was the night of the theft and recreate Franklin's actions.
In these chapters, Mr. Candy and Ezra Jennings are both shown to be specimens of that particular grotesqueness that arises out of strange contradiction. The ill Mr. Candy now has a morose appearance and a childish sensibility, yet his wardrobe and accessories are as cheerful and gaudy as they used to be. This incongruity makes Franklin uncomfortable, as he is uncomfortable with the "puzzling contradiction between [Jennings's] face and figure." Like Mr. Candy, Jennings seems at once old and young. The duality of his figure is replicated by his hair, which is half white and half dark. Mr. Candy's house, where Ezra Jennings lives, even embodies this gothic contradiction—there is a skull where a bust should be, and the fearful quality of the room makes natural birdsong seem an strange intrusion.
Ezra Jennings is an outcast figure. He occupies the margins of gender, race, and class. He self-confesses to having a "female constitution" and mixed-race parentage. He has a "gipsy complexion" and is treated poorly by his peers, yet he has the "self-possession" of a gentleman. This ability to straddle disparate social identities was also attributed to Rosanna Spearman, another outcast, who was an honest thief and a servant that had (as Betteredge reported in Chapter IV, First Period) "just a dash of something that wasn't like a housemaid, and that was like a lady." Ezra and Rosanna are also both related to the wildness of nature—Rosanna enjoyed spending time at the menacing Shivering Sands, and Jennings loves wildflowers and leads Franklin in Chapter IX to a clearing in the woods where "the lovely face of Nature met us, soft and still and colourless—met us without a smile."
Just as Rosanna figured as the outcast counterpart to Rachel, Jennings stands in as Franklin's counterpart. Jennings has been accused of a horrible crime in his past and cannot prove his innocence. In this sense, he is the ill-fated partner to Franklin, who has been accused of a crime and will succeed in proving his innocence. Jennings's exotic origins in an English colony are the counterpart to Franklin's worldly, and socially acceptable, travels in the East. Finally, Jennings stands as a figure who encompasses both scientific rationalism and objectivity, as well as feminine subjective, sensitive feeling. This indirectly evokes Franklin's preoccupation with the "Subjective-Objective" and "Objective- Subjective" sides of matters.
Many critics have remarked upon the novelty of the Moonstone's plot that features repetitive frames—an crime is committed by a man under the influence of opium (Franklin), an opium addict (Jennings) helps him recreate the crime, and the novel itself is written by another opium addict (Collins). Opium, or laudanum, in the nineteenth century was sold as over-the-counter pain medication, and Wilkie Collins took larger and larger doses of it throughout the last twenty years of his life to alleviate various complaints, including gout. In the 1871 preface to The Moonstone, Collins explains that he was suffering greatly from "rheumatic gout" while writing the middle portion of the novel and alludes to the fact that he was taking opium at the time for relief. Collins would have been concerned to depict the drug as a legitimate medicine for pain relief, and thus he sympathetically portrays Ezra Jennings as a tragic figure with a stigma unjustly attached to him because of his legitimate opium use.