“‘It all depends on what we get interested in—or what gets interested in us,’ she had added, as if this was obvious.”

Ms. Hussey’s cryptic comment implies that the material world isn’t inert, but has an active intelligence that might take an interest in human affairs. This principle asserts itself in the seemingly random clues the children receive to track the missing painting.

“What they were doing was real exploration, real thinking—not just finding out about what a bunch of dead, famous grown-ups believed. Ms. Hussey was cool.”

In this passage, Calder rejects theory in favor of exploration. Petra would agree with his view. Both children show a lively curiosity that responds well to Ms. Hussey’s unconventional teaching methods. The thief’s appeal echoes the children’s dismissal of received wisdom by encouraging the public to explore art for themselves.

“Petra loved how Ms. Hussey listened carefully to the kids’ ideas and didn’t care about right and wrong answers. She was honest and unpredictable. She was close to perfect.”

Petra shares Calder’s positive perception of Ms. Hussey. She equates unpredictability with perfection. This is the opposite of how most people would define perfection, and Petra’s unconventional approach to life is the reason that she can solve the mystery of the missing Lady.