Bestselling author Jude Watson takes Amy and Dan on a thrill-packed ride for the 4th installment of the 39 Clues.
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A Clue found in Book 3 sends Amy and Dan jetting off to find out just what's behind the fierce rivalry between the Tomas and Ekaterina branches of the Cahill family. Was a Clue stolen from the Tomas branch? Where is it now? And most important, can Amy and Dan get their hands on it before their rivals do?
It's a wild race that will take Amy and Dan deep into the bowels of the earth . . . and right into the hands of the enemy.

Never do a favor for a friend.

Twelve-year-old March McQuin forgot rule number one for cat burglars, which is how he and his twin sister, Jules, found themselves dangling upside down twenty feet above a stone floor at three in the morning. Their target was a set of stunning diamonds and it should have been an easy job, in and out. Except another thief got there first. March and Jules were lucky to escape with their lives, and one measly stone.

Now the botched heist has created a world of trouble. The stone they grabbed was the Morning Star, one of a trio of famous sapphires, and it's cursed. The theft put the twins and their friends in the crosshairs of Interpol, the FBI, and a vicious adult gang of international criminals. And worst of all, the only way to break the curse and set everything to rights is by somehow managing to steal the other two sapphires in the set.

Break out the black gloves. Lay out the masks. There's a full moon coming, and jewels to steal...

Could Amy and Dan's biggest enemy be . . . a friend? The 39 Clues Book 6 challenges everything you thought you knew about the Clue race.
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The 39 Clues gets treacherous. Book 6 takes Amy and Dan 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.