Cuff enlists Betteredge's help with the investigation and asks him to stop protecting Rosanna, as Cuff has no intention of prosecuting her. Cuff believes that Rosanna is acting as "an instrument in the hands of another person." Cuff believes that Rosanna realized that one of her gowns is stained with paint and went to Frizinghall to gather the materials to make another, which she did that night, hence the fire in the early morning hours. Cuff has followed Rosanna today to a house in the fishing village of Cobb's Hole. Cuff proposes to track the rest of her movements by her footprints in the sand. The footprints reveal that Rosanna walked into the water, perhaps to hide something.
Betteredge, having caught the "detective fever," agrees to take Cuff to Cobb's Hole to inquire at the house Rosanna visits—the house of a fisherman named Yolland, Yolland's wife, their son, and their daughter. Rosanna and the daughter, Limping Lucy, are both deformed and had become friends.
At the Yollands', Cuff drinks gin with Mrs. Yolland and gains information about Rosanna from her by being solicitous and sympathetic. Rosanna has come to the Yollands' that day and told them that she is leaving her job at the Verinder house. She used Lucy's room to write a long letter that didn't need postage. She bought a waterproof "old japanned tin case" and two dog chains from Mrs. Yolland.
Cuff assumes that Rosanna has hidden something in the tin case and sunk it in the water or quicksand, secured by the chains. He believes she has hid the stained dress or nightgown but doesn't know why she wouldn't just destroy it. Back at the Verinder house, Cuff learns that Rosanna has been back an hour and bets Betteredge that Rachel has decided to leave the house within the last hour. His bet turns out to be correct, though Betteredge refuses to believe that Rosanna's arrival and Rachel's decision to leave are connected.
Lady Verinder calls Cuff and Betteredge into her room and informs them that Rachel wants to stay with her aunt, Godfrey's mother, in Frizinghall. Cuff asks the Lady to delay Rachel's departure until two o'clock the next day, while he goes to Frizinghall in the morning.
Betteredge finally concedes to Cuff that there is something wrong with Rachel. Cuff believes that Rachel has stolen her own diamond. Betteredge begins to hate Cuff for this suspicion.