Amy and Dan Cahill's quest to find the million dollars takes them to Vienna, where they must outwit their power-hungry relatives as they seek to solve a clue involving Mozart.

Amy and Dan travel to a distant land to follow in the footsteps of their most formidable ancestor yet, a military leader who teaches them the art of ancient warfare.

Amy and Dan cross the 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.

The shadow of the man in black has followed fourteen-year-old Amy Cahill and her younger brother Dan on their worldwide search for 39 Clues that lead to a great power. The man has tried to kill them and he is a Madrigal, as were their parents. And now the man is ready to step out of the darkness for their final confrontation.

Amy and Dan Cahill learn an ultimate truth that reveals the Madrigal Mission's importance and the danger that their nefarious family members pose to the entire world.

As Cruz and his friends continue to search for the third piece of the cipher, a mysterious message arrives suggesting that someone close to him is working for Nebula, leaving Cruz unsure of who he can trust.

657 days ago Meg's British father left their home in France to fight the Nazis, leaving some codes in a jar for her to decipher, and Meg and her French mother moved to the Perche, a region in France near Normandy known for its forests; now Meg watches the German soldiers in town, and sometimes carries messages for the French resistance--but suddenly things have gotten much more dangerous: there is a wounded British officer hiding in her grandmother's...

Akiko, Mae, and Josie, also called the Infinity Trinity, spring into action after learning that a spy is betraying secrets to the Japanese military--and that Akiko's mother may be involved.--