What if Percy Jackson and Carter Kane – the stars of Rick Riordan’s bestselling mythology-inspired series—Percy Jackson and the Olympians, The Heroes of Olympus, and The Kane Chronicles – met each other? That’s a question young readers often pose to the author, and a question that Riordan has now answered in a new short story called “The Son of Sobek.” The never-before-published story will appear as a bonus in the paperback edition of The Kane Chronicles, Book Three: The Serpent’s Shadow (Disney-Hyperion), which is due out May 7, 2013. (Click here to read an excerpt from the story.)

“It’s actually something the fans had been asking me for,” says Riordan. “At least once a day I’ll get an email or a letter asking ‘Are you ever going to combine the series?’ ” So he decided to give it a try. “There are a lot of gods and a lot of characters in my books,” he says. In choosing the new work’s protagonists, “I picked two that I know very well,” he explains. “Percy and Carter are my touchstones. They represent very different sides of me. Carter is thoughtful and cautious and Percy is impetuous and sarcastic. I started to experiment with how it would be to put them together and have them join forces against a common foe.”

Riordan says he’s pleased with how the experiment turned out, and hopes his legion of devoted readers enjoys reading it. “I imagine they’ll want more and start asking ‘Where’s the rest? It’s only a short story?’ ” But Riordan has not yet decided on whether Carter and Percy will appear together in other projects. “It’s possible,” he says. “I’d love to play around with that idea, and I always like to leave some room to create other adventures for my characters. My problem is never ideas. I’ve got more than I’ll ever have time to write. It’s all about how many I can get to, and which ones readers want to see the most.”

With a broad cast of players featured in his multiple series, how does an author keep track? “I have to be careful,” Riordan says. “My readers are very detail-oriented, and if I make a mistake they’ll call me on it.” But one guiding force is the original inspiration for the books. “I stick closely to the structure of the myths,” he explains. “I may have some fun with the mythology by changing the environment to modern-day, but the structure of the myths, the monsters, the relationships of the gods – none of that is made up.” It’s a strategy that has given him confidence over the years. “I get letters from college kids who have read Percy Jackson when they were younger who tell me, ‘I just passed my Classics exam.’ The books are accurate enough that they can serve as a gateway to Homer and Virgil.”

And they’re ubiquitous enough that it’s an active gateway, indeed: together, the Percy Jackson books and The Kane Chronicles have a total of 33 million copies in print in the U.S. For now, the Kane Chronicles trilogy has concluded and Percy Jackson’s next book outing is not until The Heroes of Olympus, Book Four: The House of Hades arrives on October 8, 2013. (FOX will be releasing the feature film Percy Jackson and the Olympians: The Sea of Monsters nationwide on August 16). Riordan enjoys having the opportunity to offer readers something new in the meantime. “I think the publishing schedule is becoming more fluid,” he says “and younger fans are fairly impatient waiting for the next installment in the series they’re reading. Authors are looking for ways to make the wait a little easier. It takes me about a year to write a book, but I can create a short story in a matter of weeks. It’s a nice way to explore ideas that might not fit into a novel, and it’s a way to give readers an appetizer before the main course.”

Attendees at BookExpo America on Friday, May 31 will be privy to another appetizer of sorts as Riordan has just been confirmed as one of the speakers at the Children’s Book and Author Breakfast. “I have attended the breakfast before,” he says, “and I’m thinking about how intimidating it is going to be to follow some of the amazing speakers they have had in the past. But it will be a friendly crowd, and I will know many people there.” He particularly relishes the idea that House of Hades will make “its sneak peek debut” there. “It’s our chance to give the world the first good look at it.”

The Serpent’s Shadow (The Kane Chronicles #3) by Rick Riordan. Disney-Hyperion, paper $9.99 May ISBN 978-1-4231-4202-7