When Philadelphia detectives Jessica Balzano and Kevin Byrne are assigned to investigate the two-year-old killing of Caitlin O'Riordan, their only clue leads them into a diabolical game with a depraved killer known only as Mr. Ludo, who may be responsible for a series of disappearances from the city streets.

"Amid assignments that take the Explorer Academy recruits from the iceberg-filled waters of Antarctica to the bone-dry deserts of Argentina, Cruz Coronado is scrambling to complete the last piece of the cipher. With Nebula agents and the elusive explorer spy still out there, his opportunity to recover his mother’s world-changing formula is slipping away. But as Cruz has learned from his time aboard Orion, true explorers must never give up. Even...

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.

Scholar Jules Addison and scavenger Amelia Radcliffe join forces to unravel secrets of a long-extinct civilization, only to discover something that could spell the end of the human race.

"Forty years ago, Steven Smith found a copy of a famous children's book by disgraced author Edith Twyford, its margins full of strange markings and annotations. Severely dyslexic and wanting to know more, he took it to his remedial English teacher Miss Iles, not realising the chain of events that he was setting in motion. Miss Iles became convinced that the book was the key to solving a puzzle, and that a message in secret code ran through all Twyford's...

The heat is on as someone seems to be melting the polar ice cap. Special Agent EJ12 needs to crack the codes and keep her cool to put the evildoer's plans back on ice. That's the easy art. As EJ12, Emma Jacks can do anything. So why can't she handle the school Ice Queen of Mean Nema? Perhaps she can after all...

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.

Evil agency Shadow is up to something in the middle of the rainforest. Something that could see them get the jump on SHINE. Special Agent EJ12 needs to leap into action. She must crack Shadow's codes and foil their plan and save the rain forest. That's the easy part. As EJ12, Emma Jacks can do anything. So why is the state gymnastics meet so hard? Perhaps it isn't after all.

Emily and James discover coded notes written by Mr. Quisling and encrypted messages in Mark Twain books, and with each book triggering a fire, the team suspects that Mr. Quisling is after an unbreakable code and may be the arsonist.

One belief has sustained fourteen-year-old Amy Cahill and her younger brother, Dan, on their hunt for the 39 Clues: They are the good guys. But then a shocking discovery about their parents shatters everything Amy and Dan think they know, dividing the two siblings for the first time ever. When Dan disappears in a country of more than a billion people, Amy has to make a terrible choice - find the next Clue . . . or find her younger brother.