Guardians of the 39 Clues, Dan Cahill and his sister Amy discover that the serum is missing and must race against time to get it back before catastrophe strikes.

When an enemy finds a way to use the source of the Cahill family's power against them, siblings Dan and Amy embark on a desperate mission that will take them from one extreme of the Earth to another, but Dan may have to face the one terror he never imagined--betrayal by his own sister.

The two kids were last seen in Egypt, hunting for one of the 39 Clues that could make them the most powerful people on earth. But no one has seen the siblings since. Has the ruthless Irina Spasky finally tracked them down? Or worse-- the Madrigals? "A strange telegram lures fourteen-year-old Amy Cahill and her younger brother, Dan, deep into Russia and away from the only trustworthy adult they know. Signed with the initials NRR, the telegram launches...

Thirteen-year-old Ruby, a genius code-cracker and daring detective, gets an anonymous call setting a challenge that leads her to the headquarters of Spectrum, a highly secret anti-crime agency that needs her help to crack a code, but soon Ruby uncovers dastardly plans of the Fool's Gold Gang.

Thirteen-year-old Dan Cahill and his older sister, Amy, are running out of time. An exiled Cahill known as the Outcast has already recreated of history's worst disasters, and he's saved the worst for last. If Dan and Amy can't find and stop Outcast fast, he will initiate a full-scale nuclear meltdow.

"Charlie Thorne must search for Charles Darwin's hidden treasure in South America--with plenty of enemies hot on her trail"--