Maestro is the coming of age story of Paul Crabbe. The novel is written as a memoir, and it centers on Paul's relationship with his piano teacher, Herr Eduard Keller. Fifteen-year-old Paul has just moved with his parents from southern Australia to Darwin, in the country's far north. The story begins with Paul's first lesson with Keller, an old Austrian immigrant who lives in a room at the Swan hotel that overlooks the hotel's beer garden.
Keller begins the first lesson, seating Paul at an old, peeling upright piano and himself at a grand piano. Paul examines Keller's hands and notices that Keller is missing most of his right little finger, a fact accentuated by the presence of a gold ring on the stump. Keller refuses to let Paul play during his first eight lessons, instead spending them dispensing his musical philosophies and instructing Paul in the personalities of the different fingers. Keller tells Paul, who lightheartedly suspects that his teacher might be a war criminal in hiding, about his musical ancestry—Beethoven taught Czerny, Czerny taught Liszt, Liszt taught Leschetizky, and Leschetizky taught Keller. His parents are shocked and thrilled that Keller actually deserves the label "maestro" that others call him, and this motivates Paul's father to begin attending his son's lessons.
Paul's musical education is very important to his parents, both of whom play piano. Paul's father is a tall, stoic, quiet doctor working as a Government Medical Office. His mother, a housewife and former librarian, is short, emotional, and talkative, and the two parents disagree on everything in a half-serious, half-teasing way. Paul's parents begin hosting a Friday "soirée" night for Darwin's amateur musicians, that Keller never attends, and they join the local Gilbert and Sullivan Society.
Paul begins school at Darwin High, where he becomes a quick target for bullies alongside the other new student, Bennie Reid, who has just moved from England. Paul quickly learns to take refuge in the school's Music Room, practicing on the piano during lunch and after school. At school, Paul develops a crush on Megan Murray and begins waking up with sticky sheets. Paul tries to ask her out, but she turns him down. After school, bully Jimmy Papas beats Paul up in the bike shed for bothering his friend Scotty Mitchell's girlfriend Megan.
By Paul's ninth lesson, Keller is finally ready to let him play, but forces him to swallow his pride and begin with The Children's Bach. When Paul one day arrives at the Swan before Keller, he plays on the maestro's grand piano instead of his usual warped upright. He notices a silver clamshell frame on the piano with pictures of younger Keller, a young plumpish woman who is singing, and a child, dated Salzburg, Oktober, '27. Keller arrives and acknowledges, without detail, that the people in the photograph were his wife Mathilde and son Eric.
Paul and his parents drive south to Adelaide to spend Christmas with his maternal grandparents. He sends Herr Keller a Christmas card and receives in response a card and parcel containing a signed, 150-year old edition of Czerny's Opus 599 studies. Paul begins visiting the Adelaide University library looking for clues about Keller's past. He finds his date of birth is 1887, and one book gives his date of death as 1944, which Paul's mother passes off as a simple error. Paul makes a breakthrough when he finds a book that mentions that Keller's wife, the celebrated Jewish contralto and Wagner specialist Mathilde Rosenthal, died in Auschwitz in 1942. Fascinated by his find, Paul returns to the library the next day, where he hears the voices of a couple who have come to have sex amidst the shelves. Paul removes a large book from the shelf and watches the couple through the hole.
Paul returns to school the next year and meets Rosie Zollo, a new student from the South and the daughter of the new French teacher. Rosie instantly likes Paul and begins to spend her lunch breaks in the music room with him, but he finds her annoying. When Keller is late to one lesson, Paul looks through the scrapbooks Keller filled with newspaper clippings of tragedies and acts of stupidity. He allows Paul to take the "textbook" home but Paul's father does not let him read it. The Crabbes' Friday soirées establish a subcommittee to bring concert artists to Darwin, and their first performance is by the Brisbane Symphony. Rosie sits next to Paul at the concert, and he finds himself suddenly attracted to her. During a Wagner piece, Keller begins to shout in German and is escorted from the performance. After the performance Paul and Rosie head into the thickest region of the Gardens, where they share their first sexual experience.
Paul and Rosie's lunchtime rendezvous in the Music Room are soon interrupted when Jimmy Papas, Scotty Mitchell, and Reggie Lim bust into the room to practice for their new band. Paul impresses them with his musical knowledge and convinces them to let him join the band, Rough Stuff. Megan drives Paul to one of his practices with the band, but instead takes him by the harbor where they have sex. The experience is disappointing for Paul, and he rushes to Rosie to promise that she is the only one for him. Rough Stuff enters the Battle of the Sounds competition, with the grand prize of a trip to Adelaide for the final competition. The judge for the competition is Rockin' Rick Whiteley, the radio DJ who hosts the Drive-Time Top 40. Rough Stuff held a sit in after Rick was demoted for not playing country western music, and they easily win the competition. Herr Keller tells Paul that while he is in Adelaide he can participate in a piano competition at the Conservatorium, which he decides to enter. Keller selects a Chopin's B-Flat Minor Scherzo, which he plays from memory, making Paul realize that his indifference to Paul entering the competition is a ruse. Keller is "forced" accompany Paul to Adelaide to play the second piano for Paul's concerto.
In Adelaide Paul stays with Grandmother and Grandfather Wallace, and Keller comes to the house each morning to practice with Paul. Jimmy and Scotty arrive at the grandparents' house with Rick Whiteley instead of Reggie, who the band voted to leave behind and let Rick play drums. Before the competition Jimmy tells Paul afterward he and Scotty plan to travel with Rick looking for more gigs and a new job for Rick, who has been fired. The band performs for the last time and they go their separate ways. After a particularly long lesson, Keller spends the night at the grandparents' house. The next morning, Paul notices that Keller has six faded blue digits tattooed on his left forearm. He asks Keller about being a prisoner in the War, but Keller avoids his questions. Paul places third in the competition, and he returns to Darwin.
On his last night in Darwin, Paul visits Keller to tell him that he will study law and music performance at the University of Adelaide. Keller begins to reveal information about his son and wife, but Paul leaves because he wants to spend time with Rosie. As he walks out, Paul asks what happened to Keller's finger, and Keller says it offended him.
In Adelaide, Paul's law studies quickly fall by the wayside and he focuses on music. Mr. and Mrs. Crabbe move South during Paul's second year. For Christmas in 1972, Paul sends Keller a tape of his Honors performance but receives it back with a book full of notes critiquing his performance. Paul spends all his school holidays with Rosie at her student house in Melbourne. Paul spends the next two years traveling the world for piano competitions and trying to establish a career as a concert pianist, to mediocre results. Cyclone Tracy destroys Darwin. Keller survives by hiding under his grand piano and goes to live with the Crabbes while the city is rebuilt. While between competitions, Paul visits Salzburg, Austria. He teaches piano at a school and begins writing letters to musical acquaintances, journals, and institutions in Vienna, expressing interest in information about Leschetizky's student Eduard Keller. One response says Keller died in 1944, and the other is from cellist Joseph Henisch, who says he played trios with Keller before the war. Paul immediately packs up his things and takes the next ferry to Vienna.
Paul meets Henisch at his apartment. Henisch tells Paul that Keller and his wife met between the wars. When the Nazis arrived, Keller played for Hitler multiple times in an attempt to make himself so visible that no one could touch him or his family. However, his plan backfired, and his wife and son were captured while Keller was in Berlin for his last performance for Hitler. When Keller returned home, he sewed a yellow star to his clothing, registered as a Jew, and was sent to the Auschwitz concentration camp. Henisch, a fellow prisoner, said Keller died during a forced march of the prisoners between camps. Paul tells Heinsch that Keller is still alive and was his piano teacher. He attempts to describe Keller's style and performs for Heinsch, who remains unconvinced. Paul asks about Keller's missing finger, and Heinsch says Keller once told him that if he ever felt the desire to play again he would cut his fingers off one by one. He gives Paul a copy of Keller's last recording from Berlin in 1934 and sends him off.
After returning from his travels, Paul moves to Melbourne, where he begins teaching piano, marries Rosie, and they have their first child. In late 1977, Paul receives a letter from the sister in charge of the hospice ward of the Darwin Hospital saying that Eduard Keller was suffering a long illness. Paul flies to Darwin and goes directly to the hospital, where he finds Keller, still alive but weak and feeble. Paul spends the next few days visiting Keller in the hospital, and on the sixth morning, he receives a call that Keller has passed away. He goes to the hospice, where he slips his arm behind Keller's head and kisses him. Uncertain what to do, he tries contacting family members and friends about Keller's death to no luck. Paul returns to his hotel and dozes. He realizes Keller's death has ended his hopes of an illustrious musical career, and he both thanks and curses him for showing Paul a musical perfection that he was unable to achieve. Filled with nostalgia, Paul mourns the loss of both a great man and his own youth.