Originally published in 2006 by Running Press, Sean Stewart and Jordan Weisman's Cathy's Book is a hybrid literary work, an interactive novel that manages to work both as a teen mystery and as an interactive game with enough literary chops and facsimile evidence, Web-based clues, and cleverly embedded animation to satisfy both the writing and gaming camps.

Cathy's Book, and two follow-ups, Cathy's Key and Cathy's Ring, have sold well (120,000, 59,000, and 34,000 copies, respectively), and to attract a new audience, Running Press has developed an iPhone and iPod/Touch app. Released at the end of 2009, the Cathy's Book iPhone/iPod app managed to anticipate the current fascination with enriched e-books—online or downloadable content that uses a combination of video, animation, sound, and even multiple plot lines in addition to text—and marks the evolution of the experimental hypertext novel of the 1990s into a popular (and genuinely commercial) digital format, rich with multimedia storytelling potential.

Running Press divided Cathy's Book into three parts for the app, with the second and third apps due in May and June. Peter Costanzo, director of online marketing for Running parent company Perseus Books Group, said the first app had a couple hundred downloads, but that Running Press was waiting until all three apps were completed before launching a comprehensive international effort to market and promote the complete print and digital versions of the book together.

The original hardcover of Cathy's Book is designed to look like a journal belonging to the fictional teenager Cathy Vickers and offers clues to an unfolding mystery centered on an ex-boyfriend. The book's hip and harrowed female teen voice—the app opens with an agitated Cathy speaking on the phone—immediately evokes the usual teen alienation (and attitude) over family conflict, school, and a mysterious boyfriend, and made Cathy's Book a hit among the targeted reading group: 12- to 14-year-olds. And the prose—Stewart is an award-winning YA and science fiction author--is well written and not overwhelmed by all the bells and whistles of the app.

Costanzo said that the release of the iPhone in 2007 presented the house with a perfect platform to digitize the novel and embed video, sound, animation, and the Web within the text to tell the story. “The reader is a fly on the wall,” he said. “On the iPhone, when you're told to make a call, you get to make a real call, and kids can leave their own messages. We used a narrator that was consistent with the character in the book and worked to recreate the book's experience.” Working with app developer Expanded Books, Running Press chief marketing officer Rick Joyce, Costanzo, and Jaimee Callaway worked on the storyboards and concepts, and experimented to find the best way to preserve the print book's rich and mysterious tableau of cluttered, personalized disarray. They even embedded Wikipedia entries in the book to explain unfamiliar concepts.

The result is “a new form that kids respond to,” Costanzo said, pointing to a wealth of fan-generated material, from comments on blogs and message boards to fan-created videos uploaded to YouTube. The Cathy's Book app sells for 99 cents, and Costanzo said Running Press plans to look at different pricing and discounts.

While the house is planning to optimize the app for the iPad, Costanzo said that like all iPhone apps, it runs quite well on the iPad in its original form. And the press even issued a couple of software updates to change the structure of the e-book after readers asked for Web access from within the app. “Try retro-editing a print book,” Costanzo quipped.

He added that other publishers are taking note of the Cathy's Book app. “Publishers know Cathy's Book, and there will be more books like it.”