When an agent from Bloomsbury Publishing called grand prix rider Georgina Bloomberg asking her to co-write a novel, Bloomberg assumed there must have been a mistake. After all, she’d never considered herself much of a writer and certainly not a future author.

But when she heard the pitch—two novels centering around teenaged riders growing up on the show circuit—she knew it would be a good fit.

Bloomberg signed on to work with young adult author Catherine Hapka, and their first book, The A Circuit (Bloomsbury, original paperback, $9.99), came out in May. Hapka had a horsey background and a byline on more than 100 children’s and young adult books like The Horse Diaries series. Pairing up with Bloomberg for a novel set in the show world was a perfect fit.

The A Circuit skips over basic equestrian definitions and casually references Grand Prix jackets, high junior jumper divisions and photos in the Chronicle.

“We would e-mail paragraphs back and forth, and we’d brainstorm together about ideas,” said Bloomberg, 28. “There would be a lot of me reading something and I’d say, ‘No, actually it would happen this way,’ or ‘Let’s use this term instead,’ and we’d rework it together. It was a lot of fun.”

The A Circuit is an engaging read with coming-of-age struggles, romance and cliffhangers set against the backdrop of intense competition and barn drama. Parts may be a touch sensationalized for mature tastes (there’s an occasional canoodle in a stall and a late night post-partying high jumping competition), but the interpersonal dynamics are sophisticated enough to keep much of the book down-to-earth.

“It’s definitely for young adults, and I don’t think any adult is going to stand up and say it’s their favorite,” said Bloomberg, who lives in New York City. “But so many adults have told me they’ve really enjoyed it. I’m glad we could do something that was at least entertaining for them.”

To keep herself apprised with the concerns of those a decade and a half younger, Bloomberg hit up her teenage friends from the show circuit and from The Rider’s Closet, the charity she founded to provide equestrian clothes to riders in need. As luck would have it, Bloomberg was in the middle of reading Stephanie Meyer’s Twilight series when she started the project. This helped her understand the genre itself.

The A Circuit follows three juniors at top Westchester County show barn Pelham Lane: Kate Nilson, who “puts the working in working student”; Zara Trask, the daughter of a rock-and-roll star who’s just moved east from the West Coast; and Tommi Aaronson, whose billionaire financer father doesn’t take her professional riding ambitions seriously.

Many readers and reviewers assumed that Aaronson’s character was autobiographically inspired, as Bloomberg also grew up in the public eye as the daughter of the founder of Bloomberg L.P. and current mayor of New York City, Michael Bloomberg. But Georgina dismissed that comparison as overly simplistic, at best.

“That had never occurred to me until I started doing [promotional] interviews,” said Bloomberg. “Looking back on it I can see why people would think that, but that never came across when we were writing. When we were writing the book it really felt like there was something in every character that was a part of me. We wanted to show that even though everyone’s coming from a different background, and they’re at a different place in their lives, everyone has their own struggles, no matter how easy things seem on the surface.”

After the Lake Placid Horse Show (N.Y.) this July, Bloomberg will wrap up her season to undergo back surgery. By the time the second book in the series, My Favorite Mistake, comes out in March she’ll be back in the show ring.

“It’s easy to lose touch with why you’re doing this,” she said. “You can get so caught up in building a business and a career, you can forget how it all started and what your passion was. Writing this book brought back memories of being a kid, when all I wanted to do was get dropped off at the barn and, even if I just had one to ride, just hang out all day at the barn because I loved it so much.”