Eleven-year-old Claudia Kincade is feeling underappreciated by her parents and the world in general. The best way to teach them a lesson, she decided, is to run away from home for a while. But what she hates more than being underappreciated is being uncomfortable, and so she chooses to run away to the Metropolitan Museum of Art in New York City (for all those poofy Marie Antoinette beds to sleep in) and drags along her nine-year-old brother Jamie (for his $24.43).
Thus begins the adventure of a lifetime for both of them. Between hiding from museum security in the bathroom, doing laundry, and scrounging for change in the museum fountain, Claudia becomes obsessed with a statue sold to the museum for $225 that may or may not be a Michelangelo.
And why is the eccentric multi-millionaire Mrs. Basil E. Frankweiler writing such a long letter to her dear lawyer Saxonberg?
This story provides examples of:
- Big Fancy House: The Frankweiler mansion. Claudia is particularly impressed by the bathtub.
- Brother-Sister Team: Claudia and Jamie
- Card Sharp: How Jamie acquires all his loot.
- Catchphrase: Jamie's is "Oy, baloney!" Turns out to be helpful for Claudia to remember the city of Bologna, Italy
- The Confidant: What Claudia becomes for Mrs. Frankweiler, to both their benefits.
- Cool Old Lady: Frankweiler, who is so old and rich and lacking in fucks to give that she amuses herself by setting the Metropolitan Museum of Art on a wild goose chase simply so she can watch the fun from afar and then gives the invaluable secret of the statue to a twelve-year-old girl she's only met once solely on the basis of recognizing a kindred spirit.
- Eccentric Millionaire: Frankweiler, who sells a genuine Michelangelo to the Met for pocket change then refuses to provide authentication just so that she can watch the curators squirm.
- Epistolary Novel: The entire book is a single long letter from Frankweiler to her lawyer.
- Fancy Camping: Claudia's reasoning for choosing the Met is that she wants to run away somewhere clean and comfortable.
- Free-Range Children: Police and journalists' reaction for missing children is really muted in the 1960s compared to today.
- Grammar Nazi: Claudia has a bit of a habit of correcting her brother's grammar.
- Gratuitous French: Frankweiler offers Claudia and Jamie a lunch of nouilles et fromage en casserole...and laughs when they realize it's just macaroni and cheese.
- Long Title: From the Mixed-up Files of Mrs. Basil E. Frankweiler. E. L. Konigsburg is fond of such titles in general.
- Middle Child Syndrome: Claudia's sick of being lost in the middle of her family. She just wants to feel special.
- Non-Residential Residence: The protagonists live in the Metropolitan Museum in New York for most of the book, hiding and dodging guards.
- One Degree of Separation: Saxonberg, Mrs. Frankweiler's long-time lawyer, is also Claudia and Jamie's grandfather.
- The Runaway: Claudia and Jamie
- Senseless Violins: Claudia and Jamie packs most of their clothes in a viola and trumpet case.
- Swiss Cheese Security: The Met overnight security.
- Unusual Euphemism: Jamie's favorite minced oath is "BALONEY", which provides Claudia the Eureka Moment required to solve the Michelangelo mystery.