The powerful Cahill family will be pitted against a ruthless cabal in Scholastic’s follow-up to its multimedia franchise, The 39 Clues. The new series, The 39 Clues: Cahills vs. Vespers, launches in April 2011 with Vespers Rising by Rick Riordan, Peter Lerangis, Gordon Korman, and Jude Watson, and will wrap up in March 2013 with a seventh installment penned by bestselling thriller author David Baldacci. Vespers Rising has an announced first printing of 500,000 copies.

Continuing the multi-platform concept, the second part of the series will entail collectible cards and an online game and will include enhanced interactive features on the series’ Web site. The 39 Clues model has obviously clicked with young readers: there are more than 8.5 million copies of the original 10-book series in print, the series has been licensed for publication in 24 languages, and the Web site has more than 1.2 million registered users to date.

Asked about the incentive for creating part deux, David Levithan, v-p and editorial director of Scholastic Press and multi-media publishing, has a simple answer: “The kids wanted it.” He notes that the 10th book, Margaret Peterson Haddix’s Into the Gauntlet, which pubbed in August, “was our best launch yet. And when that book came out, the first installment, The Maze of Bones by Rick Riordan, was still among the top 10 titles on BookScan’s children’s list. The 39 Clues has engaged both readers and gamers and has created a world that kids don’t want to leave and that new kids are discovering all the time.”

Rachel Griffiths, senior editor of Scholastic Press and editor of The 39 Clues, says that the 2.0 version immerses readers into the series’ action more extensively than before. “We’ve built a huge online community and we’ve been able to interact with kids and learn so much from them,” she says. Scholastic plans to roll out moderated message boards where kids from around the world can interact and share their theories. “And this time around,” Griffiths adds, “kids have a bigger role in the story. They’ll be able to work with characters in the book to solve the story’s central mystery.”

In addition to the authors of Vespers Rising (three of whom—Korman, Watson, and Lerangis—will each contribute a subsequent novel), 39 Clues veteran Linda Sue Park and Roland Smith, a newcomer to the series, are part of the author roundup for the new series. Baldacci, whose works for adults include the Camel Club and King & Maxwell series, was a popular in-house choice to write the final novel, says Griffiths. “We are big fans of David here,” she comments. “We knew that he’d do a great job with an action adventure for kids and thought that having him write the last book would be a perfect way for him to be part of this series.”

Baldacci says he was happy to join the team. “I never thought I’d get an offer like this and it’s really very flattering,” says the author, who heard from Scholastic when he was on summer vacation with his teenage children. “They’re a bit older than the target audience, but they’ve read some of The 39 Clues books, and they thought it was kind of cool that I’d be part of it,” he says.

The author has read the existing The 39 Clues novels and looks forward to reading the new installments before tackling his own entry. Addressing the challenge of jumping into an established story arc, Baldacci says, “I’ve got to make sure I step up and tie all the loose ends together. I’m at the tail end, so I really can’t blow it, can I?”

Another challenge Baldacci faces is writing for a different audience than the readers of his popular adult novels. “Writing for kids is a slightly different process,” he says. “But in The 39 Clues there is a thriller-esque level of violence and mayhem, so I won’t have to tone that down too much. There are bodies, and some other bad things, which I’m excited about! Still, it’s a departure for me. It’s these sidelines in life that make it all worthwhile.”