When Claudia runs away from home, she does so with careful preparation, even to the point of making sure she's not "running away" but "running to" somewhere. She saves her allowance, chooses her brother, Jamie, to accompany her, and identifies her destination, the Metropolitan Museum of Art in New York City. (If you're going to run away, might as well go somewhere large, comfortable, indoor, and preferably beautiful.)
Claudia plans to return as soon as everyone has learned a lesson in Claudia appreciation and certain sibling injustices have been corrected. And, as Claudia learns later, she is tired of being boring, straight-A's Claudia Kincaid.
Claudia and Jamie's meticulous plan goes off without a hitch: supplies in their instrument cases, days in the museum, meals at the snack bar, and nights sleeping in a canopied sixteenth-century bed. Kids. Hiding out in a high security museum.
It isn't until Angel, a twenty-four inch marble statue, arrives that the learning, and the mystery, really begins. As museum officials seek to determine whether Italian artist Michelangelo is Angel's creator, Claudia and Jamie try to solve the mystery themselves and, for Claudia anyway, discover someone other than her boring, straight A's self.
When the all but forgotten race to find two missing children leads closer to Claudia and Jamie, the children are led to Mrs. Basil E. Frankweiler, the all but forgotten narrator of the story, and her mixed-up files. Given one hour to discover the truth, Claudia and Jamie devour the files as behind the scenes, their own mystery is unraveled.
(Special thanks goes out to the two girls in my class who told me that this is one of the best books they've ever read and who, in doing so, reminded me that E. L. Konigsburg's classic deserved inclusion on the site. Thanks, ladies!)