The 39 Clues, the interactive, globe-spanning series of young adult novels is drawing to a close. Nearly two years after famed YA author Rick Riordan (Percy Jackson and the Olympians) penned the first book, the final entry, Book 10: Into the Gauntlet, will be hitting stores tomorrow. So, in honor of the completion of the best-selling decalogy, EW has conducted a round-robin interview with all of the series’ authors. It works like this: We ask Riordan a question, who then asks Book 2 author Gordon Korman a question, who then asks Book 3 author Peter Lerangis, and so on and so forth. Here’s what they had to say.

Entertainment Weekly: What inspired you to work on an interactive storytelling series instead of another straightforward narrative, and was it hard for you to leave the story in other authors’ hands?

Rick Riordan: I loved the idea of making history interesting for kids! When Scholastic approached me about The 39 Clues, I immediately started going through the “greatest hits” from my years as a social studies teacher, and picked the historical characters and eras that most appealed to my students. Developing the series’ story arc didn’t take much time at all. Writing Book 1: The Maze of Bones didn’t feel much different than writing one of my other novels, but I thought it was very innovative to offer the website and trading card components as well for those readers who wanted to go more in depth with the Cahill experience. As for handing the story to other authors, of course it was hard to say goodbye to Amy and Dan, but the story has been in such good hands. Every time a new book arrives, it’s like getting a present. I get to catch up with old friends!

Rick Riordan to Gordan Korman: I’ve always found the second book in a series is the hardest to write. I imagine it would be even tougher when you’re taking over a story from another author, although you made it look effortless. How was that experience for you? Was there anything particular you did that made the story feel like your own in the two 39 Clues volumes you wrote? Anything you are particularly proud of?

Gordon Korman: Rick, you did an incredible job setting the stage for the rest of us authors. I felt like my imagination got the world’s greatest jump-start. I love everything about the multi-author dimension to The 39 Clues. Writing is a solitary job, and for the first time in my life, I have “co-workers” which is a lot of fun. I think all of the authors have put our own unique stamp on the books. I had the opportunity to revisit Austria in Book 2: One False Note, a country that I toured when I was in my 20s. I also took the characters on an adventure to China–a place I’ve researched but have never traveled to–in Book 8: The Emperor’s Code. I’ve also done a lot of research on Mount Everest so I decided to bring the action there as well. I had a lot of creative freedom writing two books in the series and I’m particularly proud of the things I’ve done with some of the minor characters, especially the “au pair” Nellie and Jonah Wizard. In my tours around the country visiting schools, a lot of 39 Clues fans have told me that hip hop artist and reality TV star Jonah is their favorite character. Because of this, I gave him a big role in Book 8: The Emperor’s Code.

Gordon Korman to Peter Lerangis: We’ve all taken Amy and Dan to cool and exotic locations, and you really seem to thrive on this freewheeling globe-trotting dimension of the series. Can you discuss the balance between research and pure imagination when crafting a story that takes place in faraway lands you’ve never visited? Is there one setting that particularly “transported” you as a writer?

Peter Lerangis: Definitely South Africa, in Book 7: The Viper’s Nest. I really wanted to swing over to Pretoria to write this book. I love to travel. During normal workdays, sometimes it feels like I have to bludgeon ideas out of my soul — but when I’m traveling, relaxed and unpressured, the ideas just spill out. There was one problem — the deadline. So I made research a form of travel. I immersed myself: reading books and magazine articles, interviewing people, listening to music, watching films. I flew over the country and zeroed in on city streets, savannahs, the veldt, and the coastline for free, thanks to Google Earth. My best voilà moment came while searching Pretoria for the perfect locale for an explosion scene, and finding a place called Boom Street. Talk about a rich and complex history—I managed to combine Shaka Zulu and Winston Churchill in one adventure, even though they lived in different eras. The whole time, I was chained to a desk in a small room in New York City…but I can still give people a pretty amazing travelogue!

Peter Lerangis to Jude Watson: Hey, Jude, we’ve all become good pals since the series started. But at the beginning Gordon and I had known each other, and neither of us knew you. It was intimidating for me to follow in Rick and Gordon’s footsteps. How did it feel for you being the fourth writer?

Jude Watson: Well, Peter, I have to confess, just between us, that I was too dumb to be intimidated. At first. As the first female author invited to the party, my inner ten-year-old tomboy just pumped a fist in the air. I was ready to mix it up with the big boys. After all, I’d written more than forty Star Wars adventures–which means I’ve written, oh, maybe a zillion lightsaber battles? So a globe-trotting adventure series set on Earth? Piece of cake. Ahem. Then I read Rick’s manuscript, and Gordon’s, and yours. I went from “bring it on” to “what have I gotten myself into.” You guys sure know how to keep the thrills coming. Was I intimidated? You bet. But one thing about this series, you can’t let down the team­–and that includes all of our readers. They’re part of the story, too. That’s a tremendous amount of inspiration. It was especially fun to bring some girl power to the series. I loved researching powerful figures in ancient Egypt like the pharaoh Hatshepsut and Nefertari in Book 4: Beyond the Grave, and then Amelia Earhart for Book 6: In Too Deep. I’d say as a general rule for a writer, if you can lock two kids in an ancient tomb with an ex-KGB villain, you’re cooking with gas.

Jude Watson to Patrick Carman: Patrick, I think of you as a cinematic writer. You keep a breathless pace, and the action sequences are visually exciting for the reader. Do you consciously think of film pacing when you write?

Patrick Carman: I’m a visual thinker, thrill seeker, and I’m easily distracted. I see everything I’m writing and I think it naturally affects the pace of things. This trait served me well with The 39 Clues, where we’re all trying to make history and geography exciting for young readers. Thinking visually worked like a charm when I had the Cahills blasting across Russia with monster trucks and motorcycles in Book 5: The Black Circle. When I was writing this book, I put the characters on a 24-hour clock to keep the action going. I wanted Amy and Dan to hit as many of the historical sites in Russia as possible. Take the Motherland Calls for example. Imagine a statue that is almost twice as big as the Statue of Liberty. I had a blast visualizing and writing about the characters climbing to the top of this enormous statue to find an important document. I wasn’t really conscious about The 39 Clues movie when I wrote The Black Circle. My job as an author is to tell the story in the best way possible, to make it flow seamlessly and get the reader to keep turning the page. But now that I think about it, I wonder if the movie version will take Amy and Dan to the Motherland Calls, or any of the awesome sites in Russia that I wrote about in the book. I hope so!

Patrick Carman to Linda Sue Park: The Cahills have been all over the world, but even ten books can’t cover every cool place on earth. If there were going to be an eleventh 39 Clues book, where would you send Dan and Amy next and what historical figure would you most want them to discover? Oh, and can I borrow eight dollars?

Linda Sue Park: I just looked in my purse. I have three dollars and twenty-seven cents. You can have it all. Or–hey, my subway card has $10 credit on it, would that help? Anything for you, sir. And what a great question! I would send Dan and Amy to Mexico because I think here in the U.S. we all need to learn more about our nearest southern neighbor. As for a historical figure: Three Mexicans have won the Nobel Prize, and I think I’d pick one of them. I can’t decide between Mario Molina and Octavio Paz. Mario Molina was a brilliant chemist whose work led to the discovery of the dangers to the ozone layer of earth’s atmosphere. If the eleventh book was about him, readers could learn more about the environment. Octavio Paz won the Nobel Prize for literature–and the Clues books haven’t yet explored a famous author. How could we writers have let that happen?

Linda Sue Park to Margaret Peterson Haddix: Margaret, in my opinion, you had the toughest job of all of us. I don’t know how you did it, and I can’t tell you how much I admire you for taking on the task. Could you describe one of your toughest challenges in writing Book 10 and how you managed to claw your way out of it?

Margaret Peterson Haddix: I think I can second Jude’s comment about having been “too dumb to be intimated.” In the beginning, I actually thought my job would be easier than everyone else’s, since I’d only have to coordinate with the books that came before mine, not any subsequent books in the series. Then reality kicked in. I realized that everybody else had set the bar really, really high for the quality of the series, and I didn’t want to be the one who ruined that, and I was the only author besides Rick who’d have to include all the major characters in my book. And even though he’d made it look easy, it wasn’t.

So, yeah, I was pretty much in a constant state of panic, paranoia and fear the whole time I was writing Book 10: Into the Gauntlet. Fortunately, that made it easier for me to identify with Amy and Dan, who were facing an even more insurmountable task.

I’d actually count two things as my “toughest” challenge writing this book. The first was something I think everyone except Rick dealt with: having to start writing the book before the book(s) right before it were in final form. I have to give credit to Rachel Griffiths, the editor who coordinated the whole series, for helping me handle this. And I was very grateful to you, Linda Sue, for being willing to make some changes in your book to help mine. The other huge challenge was figuring out a climactic event for the tenth book in a series that had already included deaths, near-deaths, death threats, explosions, shocking revelations, and more ups and downs than the most extreme roller coaster. I quickly realized there was no way I could top the rest of you. But I could do something else….