King's Ransom by Jude Watson

The 39 Clues: Cahills vs Vespers. Scholastic, 2011. ISBN 9780545298407 (Hardcover).
(Ages: 10 +) The 39 Clues series is written by multiple authors and this is the second in a spin off series. This series has two families, the Cahills and Vespers, engaged in a deadly rivalry. The main characters in this book, Dan and Amy Cahill, are forced to work their way across Europe stealing historical documents and artifacts so they can save the lives of family members kidnapped by the Vespers.
While a lot of the situations and escapes by the two teenagers are not feasible the fast pace of the narrative does allow the reader to suspend our disbelief for much of the book. The historical details are interesting but not over described and the puzzles and clues engaging. It would be preferable to have read others in the series as there are characters and events mentioned in passing that a first time reader would find confusing. There is an associated website with information and more puzzles and clues.
This is not a lighthearted read with an often depressed Dan, major betrayal by family members, and a death, so librarians may wish to monitor its borrowing by younger readers.
Chris Lloyd