One False Note is the second book in The 39 Clues series. It is written by Gordan Korman, and was published by Scholastic in 2008.
Amy, Dan, and Nellie, found music by Wolfgang Amadeus Mozart in the end of the first book, The Maze of Bones, leading them to Vienna, Austria, to learn about the composer and find a related, second clue.
In Vienna, Amy and Dan discover that Mozart had a younger sister: Maria Anna "Nannerl" Mozart and they find her diary.
They discover that there is another song in the middle of the song by Mozart named after his birtplace, Salzburg, Austria. They go there to the Salzburg Catacombs and then to Venice, Italy.
In Venice, they find a secret passage from a music store and then find the 3 missing diary pages which lead them to the second clue and two Japanese swords. At the end of the book, they buy plane tickets to Tokyo, Japan.
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