In 2001, Eoin Colfer introduced criminal mastermind Artemis Fowl to young readers, who were thrilled to make his acquaintance. That eight-book series has sold more than 25 million copies worldwide, and Walt Disney Studios will release an eponymous tie-in film in August.

Now Colfer shifts his focus to Artemis’s younger twin brothers, Myles and Beckett, in The Fowl Twins (Disney-Hyperion, Nov.).

At what point did you decide to write a novel centering on Artemis’s siblings?

I think as soon as the twins showed up in the Artemis books, my writer’s brain opened a file on them to be revisited once Artemis had completed his transformation to good guy. When I finished the Artemis saga, I gave myself five years to purge leprechauns from my brain before I would go back to the fairy world, but as it turned out, leprechauns will not be cast out.

Was it challenging to revisit Myles and Beckett as adolescents, given that you last knew them as four-year-olds?

It was a little difficult to age them up, but I always enjoy a challenge—in fact, I am not really interested in a project unless it stretches me a little bit. For me, the main challenge was to have Myles take up the criminal mastermind mantle, but to distinguish him from Artemis. After a while, it became clear to me that the best way to have Myles distinguish himself was to have him pity Artemis as a weaker intellect.

Did you find it rewarding to portray Myles and Beckett at a similar age as the book’s middle grade readers?

It was great fun, and the further I went along in the book the more I knew the characters and their quirks, so that eventually I had to go back and rewrite them with all this fresh information. I like to give the characters quirks to establish them as individuals, but also ground them a little. For example, Myles may be a genius, but he suffers from migraines.

What lies ahead for the twins?

At the moment, this is a duology, but I am very open to extending to a trilogy. I am working on book two and really enjoying myself. It is embarrassing how much I laugh at my own computer screen. I will see how the readers react. If there is an appetite out there for more Fowl stories, I would love to tell them.

Today, 8–9:30 a.m. Eoin Colfer will speak at the Children’s Book & Author Breakfast, on the Main Stage.

Today, 1–1:30 p.m. Colfer signs in the Disney booth (1713).