At the end of Chapter 34 of Oliver Twist, Oliver falls into a half-sleep near an open window, and either dreams or senses that Fagin and another man are observing and discussing him. In the first part of Chapter 35, a thorough search is made, since Oliver is convinced they were actually there and he was not dreaming, but no sign of them can be found. The matter remains a mystery until Nancy, the girlfriend of Sikes the robber, goes to see Rose Maylie in Chapter 40 and discloses to her what she has learned about the relationship between Fagin, Oliver, and the man Fagin was with when they saw Oliver, named Monks, who has referred to Oliver as his brother and who seems inspired with a passionate hatred for him for some reason yet unexplained. Rose is at first puzzled as to how to use this information, but in Chapter 41, after Oliver manages to locate his old benefactor Mr. Brownlow again, her companions and Mr. Brownlow agree to meet Nancy on London Bridge, as she has arranged, to find out how they can force more information out of Monks regarding Oliver's parentage.
Thus, the party is convinced of the truth of Oliver's vision when they receive the news from Rose about Nancy and the information she has brought, and their response is to try to learn more by meeting with Nancy in the place she has pre-arranged for such a meeting, London Bridge.