When seven members of their family were kidnapped, thirteen-year-old Dan Cahill and his older sister, Amy, got ready for the fight of their lives. But their enemy, a terrifying group known as the Vespers, remained frustratingly elusive. They stay in the shadows, picking off Cahills one by one.

And now the Vespers have landed their most serious blow yet - a blow that strikes at the very heart of the Cahill family. Because Amy and Dan discover that there's a Vesper mole in their innermost circle. Amy and Dan need to smoke out the traitor before the next hostage dies. They have just days to discover who has their back . . . and who wants to sink a knife into it.

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From Booklist

This fifth book in the 39 Clues: Cahills versus Vespers series is the work of Newbery Medal–winning Park and follows young teens Amy and Dan Cahill as they continue their worldwide quest to protect and preserve their large and illustrious family. It turns out that there’s a mole within their close-working group (thus the title), so off they go to Yale University (and beyond) to follow clues and get to the bottom of things. After one of their suspects pronounces that the brother-sister team doesn’t know a “rat’s ass” about loyalty, things get mildly violent, with a few gunshots; then tricky, with a couple boyfriend/girlfriend issues; and then dramatic, with some hostage-release attempts. All of these elements help to make this series popular beyond those interested in the more cerebral components, such as Ivy League medievalists and rare manuscripts. The corresponding online game and accompanying game cards (in the non-library edition) don’t hurt popularity either, and fans will be carried right along with a few answers and quite a cliffhanger until a different author produces the next volume. Grades 5-8. --Andrew Medlar

Review

Praise for The 39 Clues

Featured on NBC's Today Show, Good Morning America, USA Today, The New York Times , NPR's Morning Edition, Associated Press

"One blazing success." — The Huffington Post

"An interactive mystery...it's more than just a reading adventure." — Boys' Life

"This is a multi-media adventure where you also search for clues—in books, trading cards and online. Get searching!" — Girls' Life