The next day, Calder sits with Petra for lunch. He tells her he was impressed with her description of Fort’s book in class that morning, and they start talking about odd coincidences. Calder mentions that Ms. Hussey, Mr. Watch from Powell’s, and an old lady named Mrs. Sharpe were all speaking together outside his house the day before. Petra realizes that her copy of Fort’s book must have once belonged to Mrs. Sharpe.

Calder volunteers to find out more about Mrs. Sharpe’s connection to Lo!  since he works part-time at Powell’s. On Saturday, when Mr. Watch sends Calder to deliver a package of books to Mrs. Sharpe, the boy is eager to question her. Once he enters her house, Calder immediately recognizes the print on her wall as the painting that matches his grandmother’s box cover. Mrs. Sharpe tells him that the painting is The Geographer by Johannes (Jan) Vermeer. Calder then discloses that Petra has Mrs. Sharpe’s copy of Lo!. The old woman seems intrigued by the coincidence and invites both children to come to her house for tea.

On Monday, as Calder leaves for school, he sees Petra chasing a letter fluttering in the wind. She says the letter said something about an old crime and art, but she couldn’t read it all before the wind took it.