In The 13-Story Treehouse, an illustrated middle-grade novel that Feiwel and Friends published last spring, longtime collaborators Andy Griffiths and Terry Denton (The Cat on The Mat Is Flat) introduced protagonists Andy and Terry, who – not so coincidentally – are scrambling to finish a book that’s under contract. The fictional author and illustrator live in the titular abode, whose amenities (and distractions) include a bowling alley, a see-through swimming pool, an underground laboratory, and a marshmallow machine. In the sequel, The 26-Story Treehouse, the duo has added a baker’s dozen of floors onto their domicile – plus a bumper car rink, a skateboard ramp (with a “crocodile-pit hazard”), an anti-gravity chamber, and an ice cream parlor. And, yes, they have another novel to complete. 26-Story pubs April 1 with a 50,000-copy first printing. Griffiths, who like Denton lives in Australia and who is coming to the U.S. for a five-week, 18-city tour that kicks off on April 7, spoke with PW about the Treehouse series and what inspires the stories.

Did the Treehouse sequel come more easily to you and Denton than the original novel?

I’d say the second book came very organically. It was probably harder getting the first one right – there was quite a bit of experimenting and some false starts. But once we had the format decided, and realized that the series would be the perfect vehicle to address questions readers often ask us, it came into place.

So readers’ queries sparked the premise for the novels?

Yes. We deliberately worked into these books kids’ questions about the creative and collaborative process. In the first book the question we answered was, “Where do your ideas come from?” and in the second it is, “How did you two meet?

And your answer has the fictional Andy, in a purloined, swan-shaped pedal boat, first encountering Terry floating in the sea wearing inflatable underpants, after jumping from the ledge of his burning apartment building.

I thought it would be interesting to tell readers a long shaggy dog story about the most preposterous meeting ever, and that’s how the story developed. What 26-Story does is dimensionalize the characters. It gives them a backstory so readers find out who the characters are and why they’re here. The first book was more episodic, with lots of slapstick and craziness. Here, the backstories all connect.

You also include a backstory for Andy and Terry’s friend Jill, whom they rescue from an iceberg just before the three of them are captured by pirates. What inspired that turn of events?

Pirates are stock characters in children’s fiction. Everyone knows they’re bad, but kids still really like them. And after Terry is stranded in the ocean in his inflatable underpants, you think, “What worse can happen?” Well, when they’re finally rescued by a ship, it happens to be a pirate ship, and they’re in deeper jeopardy. And this pirate captain has a wooden head that can be knocked off.

Does Jill, like Andy and Terry, have a real-life counterpart?

Yes. Jill is my wife and editor, and is a crucial third presence in our collaboration. She moderates the silliness and stops it when it gets too crazy. She reminds Terry and me that we’ve got to bring the readership with us and and not just leave them scratching their heads. The fictional Jill solves many of the boys’ problems: in 26-Story, she performs open shark surgery when sharks swallow Terry’s underpants. In actual life, Jill’s role is to keep us on track, and tie everything together.

And how would you describe your and Terry’s individual roles in the collaborative process?

As with Jill’s character, much of my and Terry’s fictional personalities is anchored in real life. Terry is slightly more of the clown. He brings randomness to the process and I bring structure. When you get those two things working together it’s a very powerful combination.

Speaking of the creative process, what do you hope readers will glean from the fictional Andy and Terry’s literary endeavors?

So often when kids come to our events, they show us what they’ve written or drawn that’s been inspired by our books. With this series, we hope to suggest that ideas come from everyday life, and that’s the key to writing. And we want to show both the pleasures of writing and drawing and the terror of being close to deadline and realizing you’re not nearly finished! We wanted to show that it’s a beautiful process that combines pleasure and pain.

You don’t have to be a writer to enjoy this series, but if you do aspire to writing, we’re giving you a playful version of how you do it. Of course we’d be very happy if readers were inspired to pick up a pen after reading the books – that would be the absolute reward for us.

Based on your feedback from fans, what is it about the Treehouse books that appeals to them?

I think the illustrated format allows kids to take in a lot of information very quickly and easily, and they love the humor. So it’s those two things combined, plus the fact that as the author I’m talking directly to them, telling readers about the book that I’m writing and they’re reading. That gives the story an immediacy and intimacy

Your and Denton’s illustrated novels have been compared to Jeff Kinney’s Wimpy Kid and Dav Pilkey’s Captain Underpants books for their ability to draw in reluctant readers. Did you set out to accomplish that?

I started writing books as a result of being a high school English teacher 20 years ago and meeting 13-year-olds who didn’t have a relationship with books or reading, and who thought the weekly trip to the library was pointless. I started writing little stories for my students about my embarrassing moments. They were immensely amused by them and asked if they could write about their own embarrassing moments. So they did, and we made a book out of them and put it in the library. It let them realize that writing is sharing stories, and showed them how books can connect to – and are central to – their lives. I would never write books that told kids, “Reading is very good for you.” Instead, my novels plunge readers into fun, chaos, and surprise, and they get the idea.

Will Andy and Terry’s tree house keep growing?

The 39-Story Treehouse just came out in Australia [and is due in the U.S. in April 2015], and we’re now writing 52-Story. We’re loving expanding the series and exploring more of the questions kids ask us. The third book, 39-Story, starts with the question, “How long does it take us to write a book?” In real life, it takes a year, but in this book we come up with the idea that a “once-upon-a-time machine” can write and draw a book in a few hours – it does all the work so Andy and Terry can goof off. Of course it doesn’t work out that simply for them. There is a lot of truth running through the series in a very playful way.

Is The 26-Story Treehouse’s April Fool’s Day pub date intentional?

Actually, I’d call it a fortuitous coincidence. The fact that I wasn’t really aware of the specific pub date may symbolize the fact that I’m not really the author at all – only pretending to be. I’ve gotten away with it for 15 years, so I’m very happy about that.

There is a deeper truth there too. My first book, Just Joking!, is about an inveterate practical joker whose pranks backfire. I see a story as a type of practical joke you’re playing to get the reader to believe a scenario that isn’t true, but you try your best to convince them it is. It’s a wonderful game that we writers play.

The 26-Story Treehouse by Andy Griffiths, illus. by Terry Denton. Feiwel and Friends, $13.99 Apr. ISBN 978-1-250-02691-0