Trust No One (The 39 Clues: Cahills vs. Vespers #5)
Linda Sue Park

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.
In this fifth volume to The 39 Clues: Cahills vs. Vespers series. Amy and Dan will venture into an unthinkable adventure that will have anticipating the final volume.