"Codes can carry big secrets! Throughout history, lots of good guys and lots of bad guys have used codes to keep their messages under wraps. This fun and flippable nonfiction features stories of hidden treasures, war-time maneuverings, and contemporary hacking as well as explaining the mechanics behind the codes in accessible and kid friendly forms. Sidebars call out activities that invite the reader to try their own hand at cracking and crafting...

As the race to find the 39 Clues builds to its explosive finish, Amy and Dan must explore an ancient culture and steal a Clue guarded by thousands of the world's best-trained soldiers. It's the most dangerous Clue search yet. As their enemies crowd in, Amy and Dan find themselves separated for the first time ever. The choice lies before them - find the next Clue, or find their way back to each other.

It's no longer a game. The body count is rising. Shaken by recent events, Amy and Dan flee to a distant land and trace the footsteps of their most formidable ancestor yet: a military leader of mythic proportions. Yet just as the siblings begin to master the art of ancient warfare, they confront a dangerous enemy that can't be felled with a sword: the truth. With the stakes higher than ever, Amy and Dan uncover something so devastating it changes everything...

"Are some secrets better left buried? As Amy and Dan track the next clue to a remote corner of the world, they make shocking discoveries about the source of the Cahills' power and the mystery of their parents' deaths. And as the threat of the mysterious Madrigals grows real, one of the clue-hunters makes the ultimate sacrifice. Amy and Dan have to decide how much they're willing to risk, and what they are fighting for. Can they avenge their parents...

Cahills are being kidnapped by a shadowy group known only as the Vespers. Now Amy and Dan have only days to fulfill a bizarre ransom request or their captured friends will start dying. Amy and Dan don't know what the Vespers want or how to stop them. Only one thing is clear. The Vespers are playing to win, and if they get their hands on the Clues ... the world will be their next hostage.

Told in multiple voices, fifteen-year-old Jamaican Louisa Adair uncovers an Enigma machine in the small Scottish village where she cares for an elderly German woman, and helps solve a puzzle that could turn the tide of World War II.