A decade ago, Rick Riordan hadn’t written a children’s book. But he did have a contract to write another installment in his popular mystery series about Tres Navarre, a Texas detective whose exploits had twice won the Edgar Award. Then an idea for a book about the son of Poseidon hit Riordan like a tsunami.

In the 10 years since, the former middle school English teacher has pumped out 14 novels about Percy Jackson and his pals, and taken a side trip to Egypt in the Kane Chronicles, a series based on Egyptian mythology that is set in the same world as the Percy Jackson books. There have also been graphic novel adaptations, diaries, guidebooks, and two films.

This fall, Riordan checks into the Hotel Valhalla with Magnus Chase and the Gods of Asgard: The Sword of Summer (Disney-Hyperion), an epic of more than 500 pages about a teen who learns on his 16th birthday that he is the human son of a Norse god.

As he does with Greek mythology in the Percy Jackson stories, Riordan brings the rich mythology of Norse literature into the 21st century: Magnus travels to Nidavellir, where Taylor Swift’s “Blank Space” is playing at a bar frequented by dwarves. The Hotel Valhalla doesn’t just have a gift shop; it has its own Ikea. Thor’s hammer has a screen, on which he can stream his favorite shows from Netflix.

The kids who made the Percy Jackson books into a phenomenon are now in college, but Disney suspects that the audience for this new series will be just as enormous: the initial print run is 2.5 million. Weeks before the book’s strictly enforced October 6 release, there are already more than 700 ratings on its Goodreads page.

New Town, New Pantheon

In 2013, Riordan and his family relocated to Boston when his oldest son, Haley, enrolled in college there. The move dovetailed nicely with Riordan’s research for the Norse series. “There’s always been speculation about how far the Vikings got into North America—did they reach Boston?” Riordan says. “And there are lots of references to them here—the statue of Leif Erikson on the Commonwealth Mall, and Viking tall ships etched onto the side of the Longfellow Bridge.” Riordan even found a way to incorporate the famous Boston Public Garden sculpture inspired by Robert McCloskey’s Make Way for Ducklings into a story about saving the world from Ragnarok. “There are nine worlds in Norse mythology, and nine ducks, so I thought, ‘That’s a pretty great coincidence. I’m think I’m going to make it not a coincidence at all.’ ”

That kind of playfulness is a hallmark of the Percy Jackson series, in which Riordan often played life-or-death moments for laughs. Riordan’s new hero, Magnus Chase, is orphaned—his mother was killed in an urban wolf attack several years earlier. His sidekicks, Hearthstone and Blitz, live on the cold mean streets of Boston with him. It isn’t until his 16th birthday that Magnus learns Hearthstone is actually a Norse elf, and Blitz is a dwarf, although you can’t fault him for not recognizing that at first.

“It’s very difficult to do elves and dwarfs without harkening back to what Tolkien did, so I had to reimagine the original archetypes,” Riordan says. “One way to do that was to go back to the idea of dwarves as master builders who were wonderful with their hands, who loved to create, and make Blitz a fashion expert. I figured there had to be at least one dwarf who loved men’s fashion, right?”

Likewise, the deaf and mute Hearthstone, who dresses like “an African-American cowboy hit man,” is not your father’s elf. “He’s rubbish with a bow and arrow, can’t sing, can’t speak at all, but has become a master caster of runes,” says Riordan, who took his inspiration from a camp counselor he worked with decades ago who sang to campers in American Sign Language. “Deafness was my way into Hearthstone’s character,” he says. “I wanted to explore how someone who can only speak in sign language would communicate in an action novel. It’s one of my favorite parts of the book.”

Writing for Reluctant Readers

“It’s crazy to think that the little boy who started Percy Jackson is now a full-fledged adult,” Riordan says. The oft-told tale about Percy Jackson’s origins begins with Haley Riordan, now 21 and a college junior majoring in creative writing. A dozen years ago, Haley was a struggling student when his father, still an English teacher, retold him tales from Greek mythology with an ADD hero front and center. Haley loved the stories so much he encouraged his dad to write them down.

Riordan was perhaps extra sympathetic to Haley’s plight because he had been a reluctant reader himself, until an English teacher, Patricia Pabst, gave him the right book in eighth grade. “She gave me Lord of the Rings, and that led me to Norse mythology, and from that came my interest in Greek mythology,” Riordan recalls. “That was my doorway into becoming a reader.” It was also after reading Tolkien’s masterpiece that Riordan, encouraged by Pabst, first started writing his own stories.

That sensitivity to the kids who haven’t yet found their way into books still informs everything Riordan writes. “I want to be a considerate writer,” he says. “I consciously try to craft prose that’s clear and keeps the pages turning and will draw in not just voracious readers but the ones who will never pick up a book. Those are the ones I’m really trying to reach.”

Right now, the plan for Magnus Chase is a trilogy, but Riordan notes that “I thought the Percy Jackson books were going to be a trilogy, too” (he ended up writing five books). He’s happy to just keep writing. “Every day I pinch myself,” he says. “I never expected my books to reach this many kids. I have the best job in the world.”