Author Ally Carter is best known for her YA adventures, such as the Gallagher Girls, Heist Society, and Embassy Row series. In her middle grade debut, The Winterborne Home for Vengeance and Valor, a group of children in foster care are sent to their new home, which once belonged to a billionaire who’s been presumed dead for several years. But when they discover Gabriel Winterborne is alive and hiding in the house’s secret spaces, the children are drawn into a decades-old web of danger and revenge. PW spoke with Carter about her plans for this series, as well as her love of secret passages.

What is this book’s secret origin?

I’d been talking to people about how YA in general has changed in the 14 years since I broke in with the Gallagher Girls series. It’s a much larger genre now, and it’s just gradually inched older as time has gone on. If I were to submit the first Gallagher book now—I’d Tell You I Love You, But Then I’d Have to Kill You—most people would probably classify it as middle grade. This seemed like a good time to lean into that, and write something for younger readers, as it’s something I’ve been interested in doing for a long time.

My editor at Houghton Mifflin Harcourt is Catherine Onder. I’d previously worked with her when she was at Disney-Hyperion, where she edited the Gallagher Girls and Heist Society. We’ve been joking about getting the band back together for years. I wanted to do a big story, a swashbuckling adventure that still hit all those personal story beats, and I wanted it to also be about found family. Something character-driven. Cat had just moved over to HMH, so everything worked out perfectly.

What were your inspirations for this book and these characters?

My goal with this was to make it a dual lead story, [alternating] between April and Gabriel. I love a reluctant mentor arc. At the end of the Avengers saga, you see how Tony Stark had become something of a father figure to Peter Parker, and that’s something I’ve always loved and wanted to do. And I thought it would be hilarious if you had this guy who vanishes for years and comes back intent on vengeance—all he wants is to take revenge upon the man who killed his family, but instead he finds a bunch of kids in his house, and they’re all, “Have you thought about not doing all the murder instead?” It’s basically Batman meets Little Orphan Annie.

Gabriel comes home, but doesn’t tell anyone. He does it right, he remains dead, so it’s easier to pursue his secret vendetta. Only these kids are here, and they become his new family, to replace the one he lost 20 years ago. The idea of found family is such a classic trope in children’s literature, and it fit right in with this series. When you have a reclusive billionaire who doesn’t want kids around, the best thing you can do in my business is give him a kid. And I don’t know if I’ve ever written a book that didn’t have secret passages of some kind. Evidently, I’ve found my brand.

What was it like to make the leap from YA to middle grade?

It was really easy for me. It felt more natural than if I were to try and write something for an older YA audience, like 16- or 17-year-olds. This seems to be where I skew. I used to joke that the difference between writing middle grade and young adult is less kissing, and more fart jokes. I’m quite happy with how this has turned out. It’s all about kids with agency crawling around secret passageways and trying to right wrongs, which is my sort of thing.

How’d you come up with such a dramatic title?

The title came really early in the process. I’d been thinking about how middle grade titles in general revolve around places or character names. I’d also been reading a lot of Lisa Kleypas’s historical romances, and her latest series has a major character named Winterborne. I liked the connotations of someone who comes out of cold and darkness and grows in the process. So we played with “The Winterborne Home for this and that,” and had a long list of potential titles, but it always came back to this one. I’m seriously tempted to call the sequel The Winterborne Identity, though.

What sort of research did you do for the book?

One of my biggest concerns was to properly represent the foster system. Most of the kids in the American foster care system aren’t there because they’re orphans; it’s because their parents are in prison. So in this book, the kids are chosen to live in the Winterborne Home for very specific reasons. They’re not just a random cross-section of foster care. With April, I wanted to show that she’s had both good and bad experiences within the system, even as she holds out hope that her mother will come back someday, and she’ll find her forever home.

One of the Winterborne Home’s most engaging characters is Sadie, the resident inventor and genius. Do you have a favorite invention of hers?

For the most part, Sadie’s inventions just serve the plot’s purposes. I wanted a way for the characters to communicate, for instance, and so Sadie invents something to take care of that. It was really fun to play around with the idea of a girl genius, especially one who’s spent so much time on her own. She had all the resources she needed, but until now she’s never had friends to share her ideas with.

What’s next for you, both with this series and in general?

I’m currently working on book two, but I haven’t settled on a title yet. You can expect more wacky inventions, more swashbuckling, more heartbreak. Now that these kids have found their family, they’ll have to figure out to what extent they’re willing to go to be able to stay together. The series is situated so that if I need to wrap it up with the second book, I can, although I definitely think it could go on for a while. I’ve only just scratched the surface of potential conflicts and what the world has to offer. Beyond that, there’re some exciting things in the works, but I’m not able to talk about them quite yet.

Winterborne Home for Vengeance and Valor by Ally Carter. Houghton Mifflin Harcourt, $16.99 March 3 ISBN 978-0-358-00319-9