From the Mixed-up Files of Mrs. Basil E. Frankweiler by E. L. Konigsburg
1968 Newbery Medal
Claudia is a 12 year old girl who decides to run away from home. Being the careful planner she is, she decides to invite her 9 year old brother Jamie along. Jamie is a miser. So Claudia knows he can bring some much needed funds along. And Jamie agrees because he feels a sense of pride on being the one Claudia invites.
So the two head to New York. Claudia's plan is to live a t the Metropolitan Museum of Art until her parents learn to appreciate her. The two sneak around and hide for a few days and then Claudia sees the statue. She calls it her angel and begins a quest to prove it was sculpted by Michelangelo. Along the way she decides to visit the old woman who donated it to the museum, Mrs. Frankweiler.
Claudia is on a quest to feel special. Such a secret will do this for her.
I read this book when I was a child. It was one of my favorites growing up.