By Isabella Biedenharn
March 22, 2016 at 12:59 PM EDT
Heather Weston

Somehow, in between projects like concluding her Shades of London series and seeing the adapation of Let It Snow (co-written with John Green and Lauren Myracle) head into production as a film, Maureen Johnson has another series up her sleeve, EW can announce exclusively.

Truly Devious is a murder mystery and ghost story with a setting as chilling as its plot: An elite, though possibly haunted, boarding school called Ellingham Academy. Johnson tells us about the inspiration for the Truly Devious trilogy in an interview below — but first, here’s the book’s spine-tingling summary:

Something is wrong at Ellingham Academy: Its murderous past won’t stay in the past.

Ellingham Academy is an American institution. Students can’t buy admission, they have to earn it: these are the brightest of their generation, the thinkers, inventors, artists, dreamers, and schemers who will change the world. Ellingham is the brainchild of philanthropist and tycoon Edward J. Ellingham, who happened on a remote, idyllic spot outside of Burlington, Vermont in the 1920s, the perfect setting for his “dream school of the future.” For Ellingham, the dream ended a decade later, when his wife and child were kidnapped, then murdered, in what would become the crime of the century. Ellingham pledged everything to find the killer—he ended up giving his life.

It was an empty sacrifice: For years, the killer remained at large. He taunted the police, signing his letters Truly, Devious. Eventually, someone was caught, found guilty, and executed for the heinous crimes… but questions lingered. Why, for example, did Ellingham write these words on the day he died?

Where do you look for someone

who’s never really there?

Always on a staircase

 but never on a stair.

Every institution has its ghost stories; every school imagines itself haunted. Ellingham Academy is, officially, beyond such silliness: it is devoted to greatness, and everyone accepted achieves it.

This includes Stevie Bell, who gained her fame by solving a murder when she was thirteen years old. Clever murders don’t happen along very often, and Stevie has been struggling to find her place in the competitive atmosphere of Ellingham. Then she finds out about the decades-old Ellingham riddle: Problem solved. She’ll solve the riddle, name the real killer, and prove herself exceptional. True Ellingham material.

Her investigation into the cold case is interrupted by a fresh one. When one of her classmates, internet superstar Hayes Major, turns up dead, Stevie is the first to question the official explanation. An accident? Really? Everyone else is convinced that Ellingham’s murderous past is just that, which leaves justice up to Stevie.

ENTERTAINMENT WEEKLY: What inspired the book?

MAUREEN JOHNSON: I’ve always been a mystery addict. That’s my genre passion. I love classic mysteries in particular—straight up remote houses, impossible situations, clues, and most importantly, sleuths. The first real book I remember reading was a children’s version of The Hound of Baskervilles. I remember sitting on the living room floor, reading the scene in which Sherlock sees Watson’s reflection in the teapot. I knew this was the stuff for me. I was the kid going to the used bookstore and figuring out how to buy bags full of paperback mysteries, which I would sit and read back to back to back. I’m the person who has accidentally memorized the plots of dozens of British detective shows. This is who I am.

I think I waited for a long time to write one because I thought about it so much. But for a while I’ve been collecting up a notebook of my mystery ideas. (I’m a sucker for any that include a puzzle or a mysterious letter.) I also wrote the Shades of London series, which is a mystery. Unlike those, this one has no supernatural element. It’s straight-up sleuths and murderers.

Do you believe in haunted houses (or haunted schools)?

No, and no. But! I like ghost stories a lot, which is why I wrote the Shades of London series: The Boy in the Smoke, The Name of the Star, The Madness Underneath, and The Shadow Cabinet—and a concluding volume that will be announced!

A lot of my books start while I’m working on something else. The Name of the Star—which is about the return of a Jack the Ripper-like figure in London and a specialist group of police that can see the dead—came from research I was doing for The Last Little Blue Envelope. And while I was writing the Shades of London series, I started thinking about doing what I always meant to do—a straight-up mystery. Not supernatural. The boarding school in that book lead me to create the boarding school in this book, and a different scenario for murder.

This is a proper country house mystery, American style.

Can you give us a run-down of some of the characters?

The main character is Stevie Bell, and she is the detective of the piece. Like me, Stevie has been reading mysteries all of her life. She’s tried to master the logic, the art and science of deduction. She got her chance when she was 13. She was on vacation with her family at a yoga center (hers is a multi-generational hippie family) when one of the guests died in an accident. Except Stevie realized it was no accident, and confronted and caught a murderer. She got a burst of fame from this, and got into Ellingham Academy. And it’s because of this that she wants to investigate the Ellingham Affair, a terrible series of crimes that occurred in the 1930s.

Detectives in books always have this kind of luck—everywhere they go, clever murders take place. This would be ridiculous in real life. So when one of her classmates dies, no one really believes that lightening could really strike twice around Stevie. She’s looking into an old crime that’s been solved, and now she believes a murder has happened right in front of her?

Stevie’s classmates, her friends, the Ellingham family, and the campus itself are all part of the drama.

What are you most excited for your readers to see?

The world of Ellingham Academy. It’s a very unusual, almost magical place, built by a tycoon who wanted to open up one of the best schools in the world. It’s magnificent and strange, full of nooks and secret places—for instance, it a sunken garden that used to be a lake, full of statues of Roman gods and goddesses and a geodesic dome in the center. It’s also very hard to reach—it’s halfway up a Vermont mountainside, with only one treacherous access road.

It’s the kind of place where secrets can linger, and it’s a bad place to be stuck in a storm.

What new themes are you exploring in Truly Devious that you haven’t gotten to cover in your previous books?

The genre is straight-up mystery, which I haven’t done yet. It features crimes past and present. I’ve touched on infamous crimes of the past and the nature of media, but this one gets to internet fame and crime and justice in a new way. I’m also pretty excited about the murders, which sounded more normal in my head a second ago but I’m going to go with it.

Will Stevie be hunting the same killer throughout all three books?

This question is a little hard to answer without giving things away. I will only say that it’s a continuous story! There are also two mysteries running in this: one in the present day, and one in the 1930s. There will be a lot of twists over the three books.

What’s your writing process like? Do you outline your books, or do you just let the story take you where it wants to go? Have you planned out the whole series?

A mystery is a puzzle, so in order to write the mystery, I had to know the solution. This meant planning! Lots of planning. There are charts, maps, and outlines. With a mystery like this, I have to know what it’s all leading to and who did it and what the clues are. It’s so organized in here. It looks like a Pinterest board for organizational techniques in here. There are piles and piles of classic mysteries everywhere.

The rest is excitement and murdery goodness!

Truly Devious, the first book in the trilogy, hits shelves in Fall 2017.