One False Note is the second book in the series, written by Gordon Korman. It was released December 2, 2008. After Amy, Dan, and Nellie obtain the first clue, they and the other Cahills travel to Vienna, Austria to find a clue relating to Mozart and his sister, Maria Anna "Nannerl" Mozart. While trying to find the clue, they enter a library at Mozart's house and request for Nannerl's Diary. The librarian says the diary is stolen, and apologizes. Amy and Dan then plan to raid Jonah Wizard's hotel room when they learn he stole the diary. They manage to get inside, but Nellie accidentally leads them into the wrong room and is forced to clean toilets (since she is dressed as a maid), leaving Amy and Dan to invade Jonah's room and steal the diary, with Nellie joining them later that night. They find a warning from Grace which they don't understand.