From the Mixed-Up Files of Mrs. Basil E. Frankweiler is a novel about Claudia Kincaid who runs away from home with her brother Jamie to live in the Metropolitan Museum of Art. The two children become interested in a Michelangelo sculpture of an angel donated by Mrs. Basil E. Frankweiler. They go to Frankweiler, who has them research the angel's secret using her mixed-up files. Frankweiler leaves out one essential file and, in her will, promises the children the file in exchange for the story of their running away.
Boasting the largest collection of book summaries, BookRags is the best option for titles you can't find elsewhere. They offer all of the basics (quotes, chapter summary, characters, historical context, literary criticism) but also walk through a few major topics that recur throughout the book, which can be particularly useful for essay writing.
If you're bored by traditional book notes, try Shmoop! They write their summaries in an approachable, entertaining style. Their comprehensive offering includes chapter by chapter summaries, themes, quotes, character analysis, study quizzes, and even flash cards and infographics.