One False Note

The second installment in The 39 Clues series follows orphaned siblings Amy Cahill, 14, and Dan Cahill, 11, as they race across Europe in a globe-spanning treasure hunt. Their late grandmother, Grace Cahill, revealed in her will that their family is the most powerful in history, its members including Benjamin Franklin and Wolfgang Amadeus Mozart. Grace's will launched a contest among the family's descendants to reassemble 39 Clues whose combined secret could grant immense power. In the first book, Amy and Dan found the first clue, iron solute, and obtained a piece of original Mozart sheet music. Now, accompanied by their au pair, Nellie Gomez, and Grace's Egyptian Mau cat, Saladin, they ride a slow train toward Vienna, hoping Mozart will lead them to the second clue.

Dan finds no hidden markings in the sheet music, but Amy insists the music holds meaning. The Holt family, a physically imposing rival team led by the hot-tempered Eisenhower Holt, boards the train and hunts them down. The Holts corner the siblings in the mail car, and Amy breaks a hockey stick over Eisenhower's head, knocking him down, but his twin daughters capture them. Eisenhower strangles Dan until Amy agrees to surrender. When they open the overhead luggage bin, Saladin drops out amid shredded paper: The cat has destroyed the original manuscript. Eisenhower's outburst draws a conductor, and rather than face authorities, the Holts leap from the moving train. Dan then reveals he memorized the entire sheet music with his photographic memory and reproduces it on a napkin.

In Vienna, the siblings are unknowingly watched by Ian and Natalie Kabra, wealthy teenage rivals from the Lucian branch of the Cahill family. At their hotel, Dan compares his reproduced music to an online version of KV 617, a piece Mozart composed near the end of his life, and discovers three extra lines absent from the standard version. Amy concludes these are a secret message between Mozart and Franklin. At the Mozarthaus museum, Mozart's preserved Vienna home, Amy learns that Mozart had an equally talented older sister, Maria Anna "Nannerl" Mozart, whose diary is housed in the basement library. When Amy requests it, the librarian discovers it has been stolen.

A television broadcast reveals Jonah Wizard, a teenage celebrity and Cahill cousin, holding a press conference on the same street. Amy deduces Jonah staged the event so his absent father could steal the diary. Nellie objects to stealing it back, but Amy persuades her: The contest is all they have left. That evening, the team infiltrates the Royal Hapsburg Hotel during Jonah's DVD launch party. In Jonah's suite, they spot the diary hidden in the chandelier. Dan crashes to the floor retrieving it, alerting security, and Amy and Dan escape by jumping from a balcony onto the hotel's entrance awning.

Nellie is detained by police as a suspected fan. Irina Spasky, a Russian ex-KGB agent and rival Cahill, offers to free Nellie in exchange for what Amy and Dan took. Dan tricks her by handing over a Jonah Wizard action figure he pocketed, convincing her it is a spy gadget. Nellie returns shortly after, released by police, and the team still possesses the diary.

Nellie translates the diary, which chronicles Nannerl's talent and her marginalization as a female musician, but two pages have been cut out. Amy plays the three extra lines on a lobby piano, and a passing Austrian woman recognizes the melody as a folk song meaning "The Place Where I Was Born." Amy interprets this as Mozart pointing toward Salzburg, where he was born.

In Salzburg, the team follows Alistair Oh, an elderly Korean Cahill cousin, to St. Peter's Archabbey, where Nannerl Mozart is interred. Finding nothing at the crypt, they enter the Salzburg Catacombs in the adjacent cliff. Deep in the tunnels, Amy glimpses the man in black, a mysterious figure she has seen at previous disasters. The lights go out, and an explosion collapses part of the ceiling, injuring Dan. Groping through darkness, they discover a hidden chamber with an aged parchment bearing a German list, but it turns out to be the ancient recipe for Benedictine liqueur.

A veterinarian removes a homing device from Saladin's collar, explaining how competitors have tracked them. Amy plants the transmitter inside Alistair's hollow walking stick and discovers a document hidden in the shaft: a concert announcement placing Mozart in Venice in 1770. A passage from Alistair's perspective reveals he planted the Salzburg explosive intending only to scare the children, and his conscience is troubled.

In Venice, the team follows Jonah to a music shop called Disco Volante, where playing KV 617 in a listening booth opens a passage into a Janus branch stronghold, a secret headquarters for the artistic branch of the Cahill family, decorated with undiscovered masterpieces. Amy theorizes that each Cahill branch has a defining talent: The Lucians excel at strategy; the Janus specialize in art and creativity. Amy finds the three missing diary pages in a glass case. After Jonah retrieves them through a retinal scan, Amy threatens to spray red paint on a priceless Gilbert Stuart portrait of George Washington, then sprays paint in the faces of Jonah and his companions while Dan snatches the pages. After a chaotic escape and boat chase through Venice's canals, Dan hides the pages in a waterproof cushion aboard a moored boat named the Royal Saladin.

Ian and Natalie Kabra intercept Amy and Dan on their yacht, revealing they orchestrated the Salzburg explosion and manipulated Alistair as an unwitting ally. Finding nothing on the siblings, the Kabras' captain throws them into the freezing canal. After hours of waiting at the empty mooring, the Royal Saladin returns carrying an Italian wedding party, and Dan retrieves the pages.

The translated pages reveal Mozart was importing rare ingredients and communicating with Franklin, with Marie Antoinette as their go-between. Amy discovers marginal notes in Grace's handwriting: "The word that cost her life, minus the music" beside Marie Antoinette's name and the cryptic "D > HIC" over the name Fidelio Racco. The diary identifies Racco as a Cahill cousin who imported rare Japanese steel alloyed with wolfram for Mozart. At the Collezione di Racco, a museum in Racco's former Venetian mansion, they find a harpsichord Mozart played in 1770 and hide until closing to play the sheet music.

The Kabras ambush them at gunpoint with the standard version of KV 617, and Ian begins playing. Amy realizes Grace's note warns that the D key above high C is booby-trapped. She tackles Ian as his finger hits the key, and the harpsichord explodes. Dan flings a dart from Natalie's gun into her shoulder, incapacitating her. Amy plays the correct version on the damaged keyboard, and a section of floor drops open, revealing samurai swords forged from the wolfram-alloyed steel.

Amy decodes Grace's clues: Removing the musical letters A through G from gâteau, the French word Marie Antoinette used for "cake," leaves T and U, the old chemical symbol for tungsten, the modern name for wolfram. The second clue is tungsten. The trail leads to Japan, where the steel was forged and where Racco traveled and vanished. Amy and Dan flee with the swords, and Nellie books flights to Tokyo.

In an epilogue, William McIntyre, the Cahill family lawyer, tracks the homing transmitter to a Mozart statue in Salzburg, where Amy and Dan attached it with chewing gum. He meets the man in black and reports that the children discarded the device. McIntyre reflects that Amy and Dan may be more resourceful than even Grace imagined, as a jetliner's vapor trail stretches eastward toward Japan.