The Viper's Nest is the seventh book in The 39 Clues series. It is written by Peter Lerangis and was released 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 brother and sister, Amy and Dan Cahill, and their efforts to piece together clues left by the matriarch of the family, Grace Cahill, on her death.
The Viper's Nest follows immediately on from the events of the preceding book: In Too Deep. Shocked by the death of Irina Spasky, Dan and Amy march into danger once again. For the first they begin to question how much they trust their au pair, Nellie. Later in the book, she regains their trust.
The morse code dashes and dots along the page margins in the middle of the book reads: "There is a madrigal watching".
In the pages 39-65 above the side decorations is some Morse code. The morse code translates to 'There is a Madrigal watcher'.