This second volume in the Unstoppable series offshoot of the 39 Clues cks up where Jude Watson's Nowhere to Run (2013) left off, with the supercapable Cahill siblings, Amy and Dan, evading the superincompetent henchmen of baddie J. Rutherford Pierce and globetrotting for the next ingredient (the extinct silphium plant) in the serum that will end Pierce's powers. Pierce's worldwide smear campaign makes things difficult for the siblings and their gaggle of cousins as they head from the ruins of Tunisia into the Arctic Circle. Hirsch packs a fair amount of interesting lore into his shenanigans, and if you've got the stomach for such exclamations as "Awesomesauce!" then the series will continue to oblige you: entries by Natalie Standiford and Gordon Korman are on the way.

Cahill siblings Amy and Dan continue their dangerous mission to stop evil media mogul Pierce from world domination in the spinoff series' second and third books. Relationships are tested and loyalties questioned when Amy takes matters into her own hands in Breakaway and makes a rash decision in Countdown. Plot development feels a little sluggish, but action-heavy moments raise the stakes.