The protagonist, a boy called Paul Crabbe, is taught piano by his teacher (or maestro), Eduard Keller. Paul does not like his teacher at first, but by the end of the novel has grown to appreciate him dearly. Paul learns the limits of his own musical ability through Keller, but he also grows to understand himself and Keller enough to write the novel. Additionally, he has a loving relationship with his sweetheart, Rosie.
This book deals with the main idea of contrasts, as well as other themes. Contrasts are shown by Paul's mother and father – how they differ; Vienna and Darwin – high culture vs. low culture; Paul as an adolescent and Paul as an adult – through the continual change in narrator, as Paul changes. Paul slowly comes to realisation that he is now learning from the maestro, and that his talent starts growing day by day.
The most influential character, Eduard Keller, lost his family during The Holocaust, despite performing for Adolf Hitler in private concerts in the belief Hitler would spare his Jewish family.
For Keller, the grand piano is his sanctity and security, assisting him to deal with the horrors of the world; "safe beneath that grand piano," and likewise offering Eduard a method of deconstructing life. As Paul matures, Keller's phrasings, which seemed absurd in adolescence, ossify into a "musical bible whose texts I knew by heart" but Paul does not relate them to his life until middle-age, leaving him "smug, insufferable," throughout his life.
Keller originates from Vienna, where he was a renowned musician "becoming so visible so that nothing can touch him", therefore believing he is exempt from the effects of war. Eventually he lost his wife and son and disappeared from the country, leaving every-one to believe he was dead. Filled with remorse and regret, Keller transforms and evolves to become a completely different man, "if we are discussing the same man how different our two versions." Keller understands the frivolities and foolish nature of human society, passed onto Paul in the form of clippings from newspapers, Keller's "textbooks." "The thousands of stories of human foolishness and greed and cruelty that he had tried to patch together into some kind of understanding of his fellow beings" depicts Keller's knowledge.
When Paul initially began lessons with Keller, his first impressions were misleading, "a boozers incandescent glow", "I'd seen nothing like him before." As Paul matures, his attitudes towards the Maestro become warmer and they develop an unexpressed bond. "I slipped my arm beneath his head and kissed him" represent Paul's final realisation of his connection with Keller in death. Throughout his life, Paul took the Maestro for granted, believing his advice was "irritating – and also contradictory." After Keller's death, Paul realises the opportunities Keller had presented him. "Mourning for a great man, yes, but also mourning for myself – for times and possibilities that will never come again." Throughout the novella the tone shifts from egotism and selfishness to regret and wisdom depicting Paul's growth.
In conclusion, Maestro has the main themes of adolescence and growing up. Paul is educated about life through music and Keller's experiences in Vienna and understanding of human nature contribute to Paul's knowledge of the world. The book tracks Paul as he develops into a responsible, mature man from an obnoxious, egotistical teenager.