The 39 Clues: Unstoppable Series is the third story arc in the bestselling young adult franchise The 39 Clues. It expands the story of Amy and Dan Cahill after the first two series The Clue Hunt and Cahills vs. Vespers. The series features 4 adventure books written by bestseller authors including Jude Watson and Gordon Korman.
In Unstoppable Series, Dan and Amy face a new enemy, J. Rutherford Pierce, a powerful man who runs for president. The situation is extremely dire because the man has stolen and taken the Cahill super serum. His main plan is to achieve world domination. To prevent that plan from happening, Amy and Dan travel around the world to gather ingredients to make antidote of the serum. The quest turns out to be one that may claim their lives.
Summary of the Series
The Cahill family has a secret. For five hundred years, they have guarded the 39 Clues – thirty-nine ingredients in a serum that transforms whomever takes it into the most powerful person on earth. If the serum got into the wrong hands, the disaster would rock the world. So certain Cahills have always made it their mission to keep the serum safe, buried, locked away. Until now.