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.

A Clue found in Book 3 sends Amy and Dan jetting off to find out just what's behind the fierce rivalry between the Tomas and Ekaterina branches of the Cahill family. Was a Clue stolen from the Tomas branch? Where is it now? And most important, can Amy and Dan get their hands on it before their rivals do?

Jax and Ethan must decode an ancient Greek cipher to uncover the location of two magical urns before the urns are used to remove all faith and love from the world.

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.

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.

At the reading of their grandmother's will, Dan and Amy Cahill are given the choice of receiving a million dollars or uncovering the 39 clues hidden around the world that will lead to the source of the family's power, but by taking on the clues, they end up in a dangerous race against their own family members.

"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...

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....

Nancy encounters a mysterious saleswoman in a perfume shop, a curious man on the train, and the finds herself trying to decipher a strange code.

Amy and Dan Cahill have their final confrontation with twisted billionaire J. Rutherford Pierce, a man whose power has no limits and is one step away from being elected president.