The 39 Clues gets treacherous.. Book 6 takes Amy and Dan Cahill across oceans on the trail of a famous aviator, but they find more than they're looking for. Their enemies are becoming more vicious, and the truths they discover more crushing than ever. A hint from their parents' past puts Amy and Dan on the trail of secrets their grandmother Grace would NEVER have wanted them to know. Awful memories begin to crowd in on Amy, just as her enemies circle closer. How far would she go to protect Dan? How much of a Cahill is she prepared to be? Perhaps Grace was right — some secrets are better left buried.