Much of the first part of the novel details how Claudia and Jamie settle in at the museum: blending in with school groups on field trips during the day to get a free presentation, hiding in the restroom at closing time to stay there, and emerging at night to bathe in the fountain and sleep on antique beds. During their stay, they become fascinated with the newest exhibit: a beautiful statue of an angel, thought to have been crafted by Michelangelo. Their time and money are spent trying to find the secret of the statue, hidden somewhere in the unorganized files of the statue's old owner, Mrs. Basil E. Frankweiler, who lives in Farmington, Connecticut.