When Aiden and Meg Falconer discover that Hairless Joe, a killer and madman, holds the key to freeing their parents from prison, they decide to try and trap him, despite the dangers.
Aidan and Meg Falconers' parents are facing life in prison unless Aidan and Meg can prove their innocence, but first they must escape from a juvenile detention center and elude both the authorities and a sinister attacker who has his own reason to stop them.
Unable to return to their normal lives despite the end of the Clue hunt, new Madrigal leaders Amy and Dan anxiously prepare for a retaliatory strike by the Vespers, who kidnap a number of Cahill family members and demand that Amy and Dan steal a famous painting.
Amy and Dan Cahill's quest to find the million dollars takes them to Vienna, where they must outwit their power-hungry relatives as they seek to solve a clue involving Mozart.
An escalating race to find the 39 Clues finds Amy and Dan pursuing a Clue guarded by thousands of the world's best-trained soldiers, an effort that separates them in explosively dangerous ways.