Scholastic’s 39 Clues series is one of my favorite series for kids (and me, too). Not only did they get a group of amazing writers to join in the series’ rotation of authors (Rick Riordan, Jude Watson, Patrick Carman, Gordon Korman, and Linda Sue Park), but readers are engaged through a variety of platforms (the books, online games, and trading cards) that keeps renewing kids’ interest. 39 Clues was such a success that three spin-off series (Cahills vs. Vespers, Rapid Fire, and The Cahill Files) were born, and now a fourth spin-off can be added to the 39 Clues list of milestones.
According to Publisher’s Weekly, 39 Clues: Unstoppable is the latest spin off, which is expected to begin with the release of its first book in 2013. Korman and Watson are back on board for the Unstoppable series with Jeff Hirsch and Natalie Standiford also handling some titles. Watson also created the series’ story arch (she created the story arch for Cahills vs Vespers, too) and has recently handed in a manuscript for Unstoppable‘s first installment. The new series takes Amy and Dan on more dangerous adventures as they explore lost civilizations around the world. Book 1 will take the siblings to Western Europe and near the Middle East. Watson told Publisher’s Weekly:
“For this story, I researched ancient Troy, The Iliad, and other meaty stuff that I know kids want….Part of the plot takes place in Turkey, so I had to find out what people eat for breakfast in Turkey.
I, for one, can’t wait to see where Unstoppable takes Amy and Dan.
Simply Infatuated 
I haven’t tried reading this series yet, but I’ve heard great things, I love Rick Riordan so it may be worth giving it a try :).