39 clues ; Thirty-nine clues

Amy and Dan Cahill continue to hunt for clues while reeling from the knowledge of what happened the night their parents died, and they wonder if the end is near as they try to learn the secret behind Grace Cahill's alternate will.

Amy and Dan are separated while trying to retrieve a clue which is guarded by thousands of soldiers and worry they cannot succeed apart.

Orphans Amy and Dan Cahill, continuing their worldwide quest to track down the thirty-nine clues that will reveal the secret of the Cahill family's power, follow a link to one of the planet's strongest fighters, and have a run-in with the unreliable Alistair.

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 continue their search for the clues and cross oceans amid ruthless enemies and dangerous truths while following the trail of a famous aviator.

Amy and Dan Cahill face their greatest challenge on their quest to find the thirty-nine clues, but in order to discover the secrets of their lineage they will have to make a choice that could impact the world's future.

Siblings Amy and Dan Cahill continue their global search for the clues that will unlock the Cahill family's secret power while also working to evade Irina Spasky.

Amy and Dan, following a clue found in Book 3, set out to uncover details about the origins of the rivalry between the Tomas and Ekaterina branches of their family, not realizing they are headed right into the hands of the enemy.

Amy and Dan Cahill are in the lead to find thirty-nine clues that safeguard a great power, and are in possession of a coded sheet of Mozart's music that will help them find the next clue while their relatives follow in close pursuit. Includes cards.

Amy and Dan, members of the powerful Cahill family, try to uncover the thirty-nine clues which will reveal the secrets of their lineage and find out what really happened to their parents.