Kids—fictional ones and real-life readers—can’t get enough stories about mysterious portals. And there’s a doozy of a portal in The Darkdeep, the first in a middle grade series co-written by best friends Ally Condie and Brendan Reichs, which Bloomsbury has been describing as a blend of elements from Stranger Things, Goonies, and Stand by Me.

In the story, a group of kids in the Pacific Northwest sets off into Still Cove, a place “legendary for being dangerous,” says Reichs. They soon discover an island, and on the island they find a lake where a houseboat is docked. No ordinary houseboat, this one contains all manner of “weird stuff and cool things that kids would find interesting,” according to Reichs, as well as a spinning black whirlpool, which turns out to be: the portal. As a person passes through the whirlpool, it extracts figments of their imagination, which then start to appear on the island. “At first it starts to be fun, but later it stops being as much fun,” Reichs says.

Though Condie (the Matched trilogy) and Reichs (the Project Nemesis series) have each been widely published in their own right, it wasn’t until they bonded at 2015’s YALLWEST, and subsequently, the M.F.A. program in Creative Writing for Children and Young Adults at Vermont College of Fine Art that they decided to join forces on a project, in large part so they could still hang out together periodically. We asked them to describe what their writing process was like.

How did The Darkdeep come together?

Condie: I had an idea for a middle grade last summer and it was an idea with a boat that had a lot of crazy things in it and kids could explore it, but I thought, “I don’t really know how to write this, but I wonder if Brendan does.” I emailed him the idea and luckily he was up for it. Co-authored projects don’t always pan out. It was really exciting once he started pitching ideas and throwing them out there.

Reichs: It was not easy at first to find a rhythm but through trial and error we figured out what works best. Though there are two points of view and one is a boy and one is a girl, we did not simply cut the book in half and have one write one and the other write the other. We developed a process whereby we wrote every chapter together, we edited each other and wrote over each other, so it’s really hard to tell at this point who wrote what sentence in any particular chapter. It really is a joint effort, down to the word choice.

Have you started work on the second book in the series yet?

Reichs: We have a three-book deal with Bloomsbury, two of which are dedicated to this series and the third book is potentially a third book in this series, or the first book in a new series. We have the theme for book two and we have the outlines of our plotting coming together where we think we know what we’re going to do. But we still have some deciding to do. We’ll have a full-on retreat where we put the book together conceptually and then we’ll go home and execute it.

Condie: Brendan is the best outliner of all time. We wouldn’t have made any deadlines without Brendan, because I am not an outliner and he just killed it with that.

Reichs: I have a 6 x 6 white board in my office where I keep all my books plotted out in one place, so I’m a little bit maniacal about figuring out stories.

Did you enjoy this experience? What were some of your favorite things about it?

Reichs: It’s such a great feeling every time you look at a document you worked on and someone has made it better. It’s not like your own story where you can get down when you get in a hole. Anytime we would get in a hole the other person can sort of dig their way out of it. For all the difficulties of pairing a vision together between two people you also have the benefit of two authors working on the same story nonstop.

Condie: I wanted a book that was different and it’s such a different book because Brendan was involved. Neither of us could have written this book by ourselves. And that’s really cool.

Reichs: This book is pure fun, and not everything that we’ve done on our own has been. We are super, over-the-top, geeked-out excited about this series and we’re looking forward to taking it to market.

The Darkdeep by Ally Condie and Brendan Reichs. Bloomsbury, $16.99 Oct. 2 ISBN 978-1-5476-0046-5