The 39 Clues: Cahills vs Vespers Series is the second story arc in The 39 Clues franchise, sequel to the original series (The Clue Hunt). This fantastic young-adult series features 6 adventure books written by bestseller authors—most of the authors also wrote the novels in the original series.
The 39 Clues: Cahills vs. Vespers continues with the 4th book of the series, Shatterproof. First released in 2012, the adventurous young-adult novel is written by Roland Smith.
After performing the “dirty works” for the Vespers, Amy and Dan Cahill are now wanted criminals. However, they have to follow orders in order to save Cahill family members who are taken hostage by the Vespers. The next order for Amy and Dan is to break into Pergamon Museum in Berlin to steal the Golden Jubilee diamond. If they fail, a Cahill will be killed.