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.

Shaken by a shocking loss, Amy and Dan flee to an exotic land and trace the footsteps of their most formidable ancestor yet: a military leader of mythic proportions.

Throughout the hunt for the 39 Clues, Amy and Dan Cahill have uncovered history's greatest mysteries and their family's deadliest secrets. But are they ready to face the truth about the Cahills and the key to their unmatched power? After a whirlwind race that's taken them across five continents, Amy and Dan face the most the difficult challenge yet -- a task no Cahill dared to imagine. When faced with a choice that could change the future of the world,...

It started with a kidnapping. A shadowy organization known only as the Vespers snatched seven members of the Cahill family and demanded a series of bizarre ransoms from around the world. Thirteen-year-old Dan Cahill and his older sister Amy began a global treasure hunt, determined to bring back whatever Vesper One needed, so long as it kept the hostages safe. But when they deliver the last ransom, Amy and Dan discover Vesper One's terrifying endgame....

When Bertie the badger visits his grandfather at a retirement home for magicians, he learns that his grandfather's rabbit, Enigma, has disappeared along with everyone's magical things, and the reader is invited to help break a code to find the items hidden throughout the book. Includes a built-in decoder.

Three friends form a codebreaking service and meet a motley cast of characters including a Bulgarian spy, a man from the State Department, and a little old lady who wants her diary encoded.

After twelve-year-old Addison Cooke's uncle unearths ancient Incan secrets in Peru, he is kidnapped by a shadowy organization intent on stealing the treasure unless Addison and his friends can decipher the clues first.

Using their code-breaking skills, four middle-schoolers solve the mystery of the eccentric man who draws stick figures on his second-floor bedroom window.

Chronicles the first Vesper attack on Jan van Eyck's altarpiece at Ghent in the 1600s, then jumps to WWII and young Grace Cahill's desperate bid to save the masterwork from the Nazis.

When a new book arrives at the library with a secret code written inside, Derek, with the help of his friends, follows the clues from one novel to the next and makes a discovery that may help him get past a terrible loss.