Guardians of the 39 Clues, Dan Cahill and his sister Amy discover that the serum is missing and must race against time to get it back before catastrophe strikes For 500 years, they have guarded the 39 Clues--39 ingredients in a serum that transforms whoever takes it into the most powerful person on Earth. The serum is missing, and Dan and Amy have to get it back. The plot contains violence. Book #1