Start with a likable, down-to-earth princess who never has to clean her room, even though it drives her uptight parents up the wall.
Mix in a younger sibling -- a pompous prince who says things like, "Too bad she's not tidy and perfect like me."
Top it off with a plot twist that gives the parents and prince their comeuppance, and you've got a fetching formula for a story.
It's called "Tumble Tower," the first children's book by novelist Anne Tyler of Baltimore. It is illustrated by Mitra Modarressi, Ms. Tyler's 25-year-old daughter, who has said that "Tumble Tower" will be her mother's only children's book. That's too bad.
The star of "Tumble Tower" is a princess known as Molly the Messy, just the kind of irreverent hero children can identify with. She is the nonconformist of her family, looking quite scruffy in the royal portrait alongside King Clement the Clean, Queen Nellie the Neat and Prince Thomas the Tidy.
Molly's parents are such neat freaks that their spare crowns are aligned perfectly on their closet shelf in the palace.
Prince Thomas is worse, because he's just a kid. He is so compulsively clean that his toys are arranged by size and color.
But Molly's room is as disheveled as her helter-skelter hair. She has the tower all to herself, and has strewn her clothes, toys and books from one end to the other: "Some of her clothes had lain there so long that she had outgrown them."
She also has a habit of bringing food up to her room and leaving the remnants everywhere. Dirty plates are stacked on the windowsill, next to the orange tree that has sprouted from seed; it seems that Molly discarded a half-eaten orange there quite a while back.
Needless to say, Molly's tower drives the rest of the family crazy. But one day there's a terrible rainstorm. The palace, which is built on an island in the middle of a lake, begins to flood. By the middle of the night, the water has risen to the second floor, where the king and queen awake to find the lake "lapping at the edge of their quilt."
They rescue Prince Thomas from his room, which is also on the second floor, and climb the stairs to Molly's room in the tower. She welcomes them in. Prince Thomas is shivering in his wet pajamas, so Molly digs out a pair she has outgrown. Her father is hungry, so she gives him a leftover sandwich. "And Queen Nellie was thirsty, so Molly picked several oranges from the orange tree by her window and squeezed the juice into last week's cocoa mug."
There aren't many 5-year-olds who won't get a kick out of that scene.
Then they all climb into Molly's bed, which is lumpy with all the books she has left, half-finished, under the covers.
The next day, the flood has receded and the family -- including Molly -- pitches in to clean up the rest of the palace. And they all live happily ever after, because the king and queen and prince decide they're not going to bug Molly about her messiness ever again.
Ms. Modarressi's watercolor illustrations add just the right touch of humor to the story. A graduate of the Rhode Island School of Design, she has given the characters faces full of character. Everyone has a translucent complexion and deep-set eyes, as if the family walked right out of a Anne Tyler novel.
And Molly has a slight smile that's halfway between a smirk and a mischievous grin. She's charming -- just like the book.
Title: "Tumble Tower"
Author: Anne Tyler; illustrations by Mitra Modarressi
Publisher: Orchard Books
Length, price: 157 pages, $20