Penderwicks series author Jeanne Birdsall returns with The Library of Unruly Treasures, a lightly fantastical contemporary middle grade novel illustrated by Matt Phelan. When neither of her parents are available to care for her, 11-year-old Gwen is sent to stay with her great-uncle Matthew, whom she’s never met. While visiting a nearby library, Gwen encounters the Lahdukan, small mythical beings with eagle-like wings, and is shocked to learn that she has inherited her family’s role as the liaison between human- and Lahdukan-kind. As Gwen uncovers more about the Lahdukan’s lore, she despairs over her imminent return home to her parents. In a conversation with PW, Birdsall spoke about her literary influences, the importance of belonging, and moving on from the Penderwicks.

The Library of Unruly Treasures is the first squarely middle grade novel that you’ve published since The Penderwicks at Last in 2018. What prompted this return to form?

I actually started working on The Library of Unruly Treasures as soon as I was done with The Penderwicks at Last, so it wasn’t so much that I wandered away from middle grade, it just took me a while to get this one right.

When he was quite young, a friend of mine’s son asked his dad why boy fairies don’t wear skirts. And we laughed, and I thought, “Oh, that’s such a great question.” That night, when I was trying to go to sleep, this image of a small, winged person wearing a kilt came to my brain, and I thought, “That’s my next book.”

That was something like 12 years ago. There were huge things that had to change when I finally started writing, including the fact that you can’t really fly in a kilt.

What was the inspiration behind fantasy elements like the Lahdukan?

From the very beginning of writing the Penderwicks, I knew that I wanted to write a whole series of novels. I put so much of my own family and my own hopes and dreams and needs into the Penderwicks. And it took me such an unbelievably long time to accomplish that, as I got older, I knew I wasn’t going to do something like that again. So I knew that my next novel was definitely going to be a one-off, and I also knew that I wanted to do something in the realm of cozy fantasy.

Growing up, I read so much E. Nesbit and Edward Eager. The Borrowers by Mary Norton was one of my favorite books. And when I was 10 or 11, my friend Susan Hill and I pretended that going through these two close-together trees on the fifth-grade playground would take us to Narnia. Even though we were old enough to not believe it could actually happen, there was still that strong desire to have another reality just out of reach—if only you could just find it and see it or touch it.

The most fun and the biggest challenges were probably the same thing: creating a backstory and history of who the Lahdukan were and how they got to America. What language would they speak? Originally, I wanted them to be from Scotland and live in the highlands and speak Gaelic, but it turns out that Gaelic is the hardest language in the universe to learn. Then a Gaelic scholar I spoke to said, “Make up your own language.”

How do you think the years you spent working on the Penderwicks informed The Library of Unruly Treasures?

While I was writing the Penderwicks, the characters always had a strong sense of home and family, and so they kept opening their home to other people. We have enough room in our family for Jeffrey; now we have enough room in our family for a stepmother and stepbrother. The Penderwick children aren’t looking for a home because they already have one, but they’re looking to continually redefine their home to include more and more people. But for Gwen, it was different. I sort of went in the opposite direction for Gwen’s story.

Very early on in the process of writing The Library of Unruly Treasures, I heard this story about a police officer in Savannah, Ga., who was tweeting out his experiences as a beat cop. This one story he told was about being called to a home for a domestic dispute. When he got there, there was this one little girl surrounded by a bunch of grown-ups yelling at each other about who was going to take care of her, and none of them wanted to. And this child put her hand in the policeman’s. She was living in a tumultuous enough world that the stranger—the cop—was the safest person and in the room for her.

I don’t know what happened after that, but it stayed in my brain for Gwen. There really are children who nobody wants, and they have to live with the knowledge that their family wishes they weren’t there.

Did you always envision this book as having illustrations?

I very much wanted them. In fact, I was writing the book with Matt Phelan in mind, because we did a picture book together years ago [Flora’s Very Windy Day], and there was a lot of flying in it, so I already knew how well he was with movement. Not only can he illustrate flight beautifully, but he’s also really good at rendering a lot of emotion even in just the positioning of the figure, the very simple visuals of how they’re holding themselves. I don’t know how he does it. I couldn’t possibly break it all down, but he’s a genius.

What’s next for you?

I’m not quite sure. There are a lot of things I don’t know about my future projects, but I’m almost 100% certain that my next book won’t be a middle grade novel. I can also tell you that I’ve been reading a lot about the mafia, and about Italy in WWII, and about the movie industry in the 1960s.

The Library of Unruly Treasures by Jeanne Birdsall, illus. by Matt Phelan. Knopf, $17.99 Aug. 5 ISBN 978-0-525-57904-5