From the back cover: The race is on to find 39 Clues that safeguard a great power, and fourteen-year-old Amy Cahill and her younger brother, Dan, are shocked to find themselves in the lead. The search seems to be taking them to Vienna, and they hold a coded piece of Mozart's sheet music that's key to finding the next Clue. But tailed by a pack of power-hungry relatives, Amy and Dan can't see if they are sailing toward victory – or straight into a deadly trap.

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.