The novel’s protagonist, 12-year-old Claudia Kincaid is the eldest of four children in her family. A meticulous planner, Claudia is rules oriented to a fault. As the novel opens, she dutifully fulfills her domestic and academic responsibilities but feels that something is missing; she suspects that something is increased recognition from her parents and siblings. Putting her excellent planning skills to work, she carefully plots to run away from home. As she puts her plans into action, however, she realizes that she wants to change herself, not just teach her parents to value her more. With “ambitions […] as enormous and as multi-directional as the museum herself” (47), Claudia struggles to know what form or direction such change should take.

Through her adventures in the museum and with Mrs. Frankweiler, Claudia learns about herself and manages to focus her efforts. The mystery surrounding Angel provides a focal point for her efforts, but to some extent, Angel is irrelevant to Claudia’s maturation. As Mrs. Frankweiler explains, “She would solve its mystery; and it, in turn, would do something to her, though what this was, she didn’t quite know” (65). Prone as Claudia is to worry and seek explanations for everything, she never fully articulates how she hopes to change, but she sees Angel’s mystery as a chance to become a “heroine” by making a “discovery” (118).