The 39 Clues, the interactive, globe-spanning series of young adult novels is drawing to a close. Nearly two years after famed YA author Rick Riordan (Percy Jackson and the Olympians) penned the first book, the final entry, Book 10: Into the Gauntlet, will be hitting stores tomorrow. So, in honor of the completion of the best-selling decalogy, EW has conducted a round-robin interview with all of the series’ authors. It works like this: We ask Riordan a question, who then asks Book 2 author Gordon Korman a question, who then asks Book 3 author Peter Lerangis, and so on and so forth. Here’s what they had to say.