It is the famous capital M that they are known for in the book series.
Want to become part of the Vesper Resistance? Want to help keep the secrets of the Cahills stay a secret? All you Cahills join forces and repel the despicable Vespers. Join the crew by entering my card code P3RRTJNRXP! Join the resistance!
You become a madrigal by completing Mission 10 on the 39 Clues site.
You can if you have all cards and complete mision 10
you need all the clues
When all 39 clues are put together, they reveal the ingredients needed to create the ultimate serum that grants its user incredible power, intelligence, and abilities. This serum is the key to ruling the world and has been sought after by multiple powerful and wealthy families throughout history.
Tikal, Guatemala.
it already came out
It already came out.
Same as Book 10.
In mission 10 of The 39 Clues series, the NRP is the National Rescue Project, an organization that plays a key role in the story.
In Mission 10 of The 39 Clues, the clue is "Water." This clue leads the Cahill siblings to a location related to water where they must uncover the next part of their quest.
I'm still working on it, but you have to have all the Clues in order to do the second part in Mission 10.
go read the books.