Claudia feels overlooked and bored with her life, so she decides to do what any normal twelve-year-old would: run away.
She can't go alone, so she picks her brother Jamie to go with her because he is rich (in kid's terms, at least).
The siblings take the train to the Met, and start their daily routine: wander around and join tour groups during the day, hide in weird exhibits at night, and try to spend as little money as possible.
Claudia decides that they're going to try to learn something new each day in the museum. They start with the Renaissance.
That's when Claudia sees the angel statue for the first time and is immediately smitten. She finds a New York Times and learns that the angel's origins are unknown. And that's that. She decides that she and her little bro will solve the mystery.
After a false alarm of discovery, Claudia is devastated and cries. Then she picks herself back up and heads to Farmington, Connecticut, where Mrs. Frankweiler (original owner of the statue) lives.
At Mrs. Frankweiler's house, Claudia and Jamie search (with her permission, of course) until they find the file on the angel statue. Now that she finally has the proof, Claudia cries because she is so overwhelmed.
Mrs. Frankweiler says she will give them the documents in her will. Before heading home, Claudia and Jamie sit down to tell her everything about how they ran away and what they did.