One False Note
One False Note is the second book in "The 39 Clues" series. It is written by Gordan Korman, and was published by Scholastic on December 2, 2008. Following the events of "The Maze of Bones", the protagonists Amy and Dan Cahill learn about Mozart and travel to Vienna, Austria to search for the second clue in the 39 Clues competition. "One False Note" entered the Children's Books New York Times Best Seller list at number one on December 21, 2008 and stayed on the list for children's chapter books for 12 weeks.
The Viper's Nest
The Viper's Nest is the seventh book in The 39 Clues series. It was written by Peter Lerangis and was released by Scholastic on February 2, 2010. The 39 Clues series is intended for children aged 8–12, and takes the form of a multimedia adventure story spanning 10 books. The stories focus on a brother and sister, Amy and Dan Cahill, and their efforts to piece together clues left by the matriarch of the family, Grace Cahill, upon her death.