Nothing happens that night. In the morning, Cuff confronts Franklin about what Rosanna said to him earlier; Rosanna happens to be in the bushes, and upon hearing that Franklin has no interest in her, despairingly goes back to the house with Penelope. Penelope tells her father that she is uneasy about Rosanna, and tries to console her; they consider calling the doctor’s assistant, a Mr. Jennings, but Lady Verinder is occupied.
Cuff returns from a visit to Frizinghall to talk to the Indians. He reports that the Indians do not have anything right now, but they are certainly after the Diamond. He has also found out that Rosanna went to buy cloth to make a nightgown, and that her original one must be hidden. They suggest going down to the Shivering Sand, where it is likely the tin box bought from the Yollands is hidden. Cuff suspects that something revealing is in the tin box. However, he first wishes to speak to Rachel before she leaves. The girl speeds off in the coach before Cuff can speak to her. She rebuffs Franklin as well, and he, brokenhearted, prepares to take the train away.
The man watching Rosanna has lost track of her; Nancy the kitchen maid reports having seen Rosanna slip out with a letter in her hand. They plan to go to Frizinghall to check the address of the letter at the post-office, but receive new information at the stables that Rosanna was running down to the seashore. They go to the Shivering Sand and find that the footsteps lead into the quicksand, and based on tracks, that she committed suicide.
The house is in distress and commotion over Rosanna’s death. Franklin prepares to leave, and finds out about Cuff’s suspicions of Rachel. Cuff tells Lady Verinder all of how and why he suspects Rachel, based on her behavior, and the possibility of her leading a double life and having debts to pay off. Cuff believes that she used Rosanna, knowing that the girl has a questionable past. Lady Verinder, of course, does not believe him, but agrees to let Cuff tell Rachel of Rosanna’s suicide, to observe Rachel’s reaction. She agrees on the condition that she is the one who tells Rachel herself. Franklin, not having left yet, mopes over Rachel’s treatment of him; Lady Verinder travels to London to see Rachel and sends back a letter saying that Rachel has never spoken a private word with Rosanna Spearman during the girl’s employment at the estate. Before leaving the house, Cuff makes several predictions: the Yollands will come up, the Indians will make news, and a Septimus Luker will become involved.
Soon, Limping Lucy Yolland comes with a letter to give to Franklin Blake from Rosanna Spearman, angrily declaring that Franklin was the cause of Rosanna’s death. Limping Lucy also breaks down and tells Betteredge about how miserable Rosanna’s life was. Lucy refuses to give the letter to Betteredge, saying that Franklin must get it from her himself.
Not much later, the other two predictions come true, with a Septimus Luker, a pawnbroker in London, being annoyed with three Indians milling about his house.
Sergeant Cuff plays a questionable card when he gets Franklin Blake to talk about Rosanna Spearman. He knows that Rosanna has interest in the gentleman, and that she has spoken to him, but not much else. However, when he is questioning Franklin in the garden, he purposefully asks Franklin if Franklin has any interest in Rosanna. He knows, of course, that the answer is “no,” but he asks loudly anyway so that Franklin’s negative answer is heard by the girl hiding in the bushes. He does so, most likely, to move the investigation forward. It does, indeed, but not in a way that is really expected—Rosanna kills herself. The only expectation of this happening is perhaps from foreshadowing in the earlier part of Betteredge’s narrative, when the old servant finds the girl at the Shivering Sand.
When Joyce, the policeman appointed to watch over Rosanna (whom Penelope and Betteredge are now worried about), loses her, Cuff immediately goes in search of her. This turn of events is also reminiscent of the Road Hill House Murder, when the police officers scheduled to watch over the bloodstained nightgown in the chimney failed to do so. The nightgown disappeared—and so does Rosanna.
Rosanna, Penelope, and Rachel are all around the same age, yet their lives and their outcomes are all very different. When Rosanna is found to have committed suicide, Betteredge immediately thinks of his own daughter: “My girl was just her age. My girl, tried as Rosanna was tried, might have lived that miserable life, and died this dreadful death" (197). The three girls are all counterparts to each other in terms of social class; between Penelope and Rosanna there is the difference of a family member’s love.
Sergeant Cuff finally openly tells Lady Verinder that he suspects Rachel of stealing her own Diamond for dark purposes. Like Mr. Kent in the Road Hill House Murder, Lady Verinder does not believe that her own child would do such a thing. After Constance went to trial after her accusation, her father provided a lawyer for her defense (this lawyer ultimately overturned her accusation). On hearing Cuff’s suspicions, Lady Verinder agrees to ask Rachel about Rosanna, but dismisses the Sergeant and retires to London with her daughter to get away.