One False Note (The 39 Clues, Book 2)

Amy and Dan made the choice of a lifetime when they gave up a million dollars in favor of a Clue and joined a competition unlike any the world has ever seen. After barely escaping Paris with their lives, now they're in Vienna to discover the truth about their famous ancestor, Wolfgang Amadeus Mozart, and the long-buried secrets connected to his equally talented but overlooked sister, Nannerl.

But with their enemies closing in, Amy and Dan must decide how much they're willing to risk to find the clues, and who they're willing to betray in the process...