Maureen Johnson is having a brilliant career. She is the author of more than a dozen YA novels, with over two million copies sold worldwide. Her collaborations with Cassandra Clare and with John Green and Lauren Myracle have yielded multiple books and a hit film on Netflix (Let It Snow). As a special badge of honor, the American Library Association has listed her novel The Bermudez Triangle, featuring a relationship between two girls, as frequently challenged; Johnson is now the New York/Connecticut co-chair of Authors Against Banned Books.

Johnson’s latest mystery, Death at Morning House (HarperTeen, Aug. 6), echoes several elements of her much-loved Truly Devious trilogy: Along with six murders, the novel also features a 1930s cold case plus unfolding mayhem in the present and a diverse crowd of teens, including a character with an interest in podcasts. Well, writers do have their obsessions, and to that list, Death at Morning House adds a setting that Johnson has been dreaming about since she was a girl. We talked to her about that and other matters on a recent Zoom call; we reached her in London, fresh from a meeting at her U.K. publisher. Our conversation has been edited for length and clarity.

Tell us about your road to writing YA fiction.

I kind of fell into it, almost on a dare. My closest friend, Kate Schafer Testerman, was my roommate in college; then we lived abroad together and moved to New York together. I was in grad school at Columbia, doing two MFA programs at once, dramaturgy and narrative nonfiction, which any child can tell you is a very silly thing to do. Kate got a job at a literary agency, Janklow & Nesbit. She said, “I have something I want you to try: a novel for teenagers.”

“Well,” I said, “I would never be able to write that, and to prove it to you, I’ll write a little bit of it.” Suddenly I had The Key to the Golden Firebird, my first novel. It was that fast.

I went to a Catholic girls’ school, and I wasn’t allowed out for my entire teenage years, so all I ever did was try to find the escape route. It turns out that “I gotta get out of here” and “Who are these people, and why are they in charge?” are really good places to start.

Did you also finish your master’s thesis?

Dramaturgy, no—though I had most of the credits—but nonfiction, yes. It was on the idea of staging worlds, or pretending in reality. I found the woman who created the first Renaissance faire and spent a week interviewing her. And I wrote about my first job in New York, in a haunted house–themed restaurant.

What a cool idea.

Thank you. I hope to include it in the book of essays I’m going to write just as soon as they put more hours in the day. I’m perfectly happy to write all the time.

Let’s talk about Death at Morning House. Tell us about your main character.

Marlowe has been in love with her classmate Akilah all through high school. She finally asks her out, and the date is going so well that she suggests they go out to a little cabin on the lake that she’s taking care of. She’s gotten Akilah a petrichor-scented candle—it smells like the air after a storm. She lights the candle, they start making out…and just then, the candle explodes, the curtains catch on fire, and the cabin burns down.

Poor Marlowe is so freaked out that she leaves town.

She gets an opportunity to be a tour guide in [the St. Lawrence River’s] Thousand Islands, at a house that was built by a very rich family, but abandoned in the 1930s after two of the kids died on the island in separate accidents on one day.

The setting is so important in this story, and evoked in such gorgeous detail. Had you spent a lot of time there?

No, I’d never been. When I was growing up in Philadelphia, people would always talk about going there, and I’d read about it, but when I decided to set the book there, I finally got to go. I was scheduled to fly up there the day of the great Northeast fire—the one in 2023, with all the smoke—and had to postpone my trip a week. But since fire is so important in the book—

—it was a sign!

I thought so. Anyway, when I finally got to the Thousand Islands area, it was so ridiculously beautiful. The water is so clear and pure. It looks tropical; it glows green. Some of the islands are only big enough to have one house on them, or one tree. In the summer, everyone hangs out on the river, going from island to island. I met a teenager who leads a boat tour. She commutes to work on a Jet Ski. I gave the kids in the book that kind of life.

And as I always do, I did much more research than I could ever actually need or use. Currents. Depths. History of the islands. Lore about pirates and buried treasure.

Do you do all your plotting in advance, or does some of it come to you as you’re writing?

The first thing I do is develop the crime. I always, always, always start with the why and the how. I’m very precise: I write entire solution documents and work from there, backward and around. And as you start pulling out threads, you figure out how justice will be served.

Murder mysteries are more than just solving the puzzle, though—that’s a part of them I love. Let me show you something. [Pulls out a binder, starts leafing through.] This is what we were working on this morning at my publisher. It’s a dossier murder mystery, which was a thing in the 1930s. You get pages of documents, pictures, newspaper articles, fake New Yorker pieces, poison pen letters—just evidence, no narrative. You work out the crime based on that, then open the sealed solution document at the back and see if you’re right. This one’s called You Are the Detective: The Creeping Hands Murders, and it’s coming out next year.

How fun! Can you tell us some of your favorite authors?

Well, I’m very lucky, because many of my favorite authors are my best friends. Back when I started, John Green and Emily Jenkins and I used to sit in a coffee shop together from 9 to 5 every day.

These days, Holly Black, Cassie Clare, Robin Wasserman, Leigh Bardugo, Kelly Link, and I work together. We live all over the place but talk constantly. If you’re stuck in the middle of the night on a problem with your book, you can call Holly. She’ll say, “Send it to me,” and she’ll call me at 4 a.m. She always knows what’s wrong, and it’s never what you think. She’s like the Dr. House of books.

A couple of times a year, Cassie rents a house in Mexico, or France, or we all go to Amherst [Massachusetts], and we write together. These are my people, my ride or dies, and they’re also really brilliant writers. It’s a beautiful world I’ve landed in. I’m very lucky.

Marion Winik hosts the NPR podcast The Weekly Reader.