An old man, Antonio Salieri, screams multiple times that he killed Mozart. His servants, hearing his cries, try to coax him out of his chamber with food, but he refuses their request. Suddenly, they hear a loud thud and barge into his chamber. In the room, they find Salieri on the floor bleeding. He has slit his throat. Salieri's servants with the help of others immediately carry his bleeding body toward a medical facility.
Salieri survives his fatal wound, but ends up in a mental institution. In the mental institution, Father Vogler, a young priest, visits Salieri, hoping to offer him relief from his troubling thoughts. Salieri asks Father Vogler if he has a background in music. When Father Vogler reveals that he studied music in Vienna in his youth, Salieri plays a few notes on the piano and asks him if he has heard of the piece. When Father Vogler says no, Salieri is visibly hurt and reveals that he wrote the piece.
Salieri plays another set of notes for Father Vogler. The priest does not recognize this piece as well. In frustration, Salieri asserts that he was once the most famous composer in Europe and that he wrote forty operas in his lifetime. Salieri then proceeds to play one last set of notes. This time, Father Vogler recognizes the piece, calls it a charming piece, and tells Salieri that he had no idea that Salieri wrote it. Salieri tells him that Wolfgang Amadeus Mozart wrote the piece. Father Vogler takes this opportunity to ask Salieri if he really killed Mozart. In response to the priest's question, Salieri begins to talk about his past. From this point on, the film transitions into Salieri's past, and Salieri provides voice over for the scenes.
As a teenager, Salieri is passionate about music but his domineering father makes it hard for him to pursue his passions. Salieri's father does not like music and views Salieri's hero, Mozart, who is years younger than the teenaged Salieri and performing for royalties, as a trained monkey. Young Salieri is envious of the fact that Mozart's father taught Mozart music. Finding his dream of being a musician out of reach, young Salieri makes a promise to God. He promises to be chaste and devoted to God if God makes him a famous composer whose name and work transcends time. Not long after his prayers, Salieri's father chokes on food and dies. Salieri views this event as a miracle and an answer to his prayers.
The death of his father allows young Salieri to study music in Vienna. After many more years, Salieri becomes a tutor to Emperor Joseph II of Austria. The emperor has no ear for music, but Salieri does not mind because the emperor admires his music. Throughout this time, Salieri keeps his promise to God. He does not give into women or other indulgences. He even gives free music lessons. Salieri's life in Vienna is wonderful until Mozart comes to the city.
At Prince-Archbishop Colloredo's residence, Salieri sees Mozart for the first time. When Salieri visits a room filled with food, a young woman enters and hides under a table. Salieri quickly hides before she sees him. A young man with a high-pitched laugh quickly comes after the young woman. The young man and young woman are inappropriately affectionate with each other. They stop when the young man hears music and dashes out exclaiming that they have started playing his music without him. From this statement and the performance that follows, Salieri realizes that the young man is Mozart, and he is in disbelief.
After performing, Mozart has a private showdown with the prince-archbishop. He wants to be dismissed from the prince-archbishop's service, but the prince-archbishop refuses to let him go and orders him instead to return to Salzburg. Mozart storms out of the prince-archbishop's residence, and snatches his music sheets from Salieri's hands on the way out. Salieri admires Mozart's music, but he dislikes Mozart's personality from this encounter and from what he witnessed in the room filled with food. He sees Mozart as an obscene child and questions why God has chosen him as an instrument.
Emperor Joseph II has a conversation with influential figures in his court (Baron Van Swieten, Kapellmeister Bonno, Count Orsini-Rosenberg, and Salieri) about Mozart. The emperor asks them what they think about Mozart. Baron Van Swieten and Salieri admire Mozart and want the emperor to hire him while Kapellmeister Bonno and Count Orsini-Rosenburg tell the emperor that Mozart is subpar and that operas should only be done in Italian. Count Orsini-Rosenberg and Kapellmeister Bonno's negative responses appear to come from jealousy of Mozart. In the end, the emperor agrees to have Mozart as part of his court. A big reason for this is because Mozart's presence in Vienna would irritate the prince-archbishop.
When Mozart comes to the emperor's palace, nervousness causes his high-pitched laugh to be even more exaggerated. He shows respect to the emperor and flatters all of the pivotal players in the emperor's court, except Salieri. In front of the emperor and the influential members of his court, Mozart calls one of Salieri's old pieces a funny little tune. Furthermore, Mozart demonstrates the flaws in a piece that Salieri wrote to welcome him to court and improves the piece on the spot. This encounter makes Salieri question once again why God has blessed Mozart with exceptional talent.
Salieri thinks it is unfair that he has lived a chaste life and merely mediocre skills, while Mozart is immoral and vulgar, yet a genius. God and Mozart deal another blow to Salieri. Mozart gets his wish to write a German opera whose setting is a Turkish harem, and he chooses as his lead actress, Katherina Cavalieri, the woman who Salieri admires. Salieri is affected by the casting; but something more painful and shocking takes place soon afterwards.
Mozart's characteristics contradict each other. Mozart has adult desires, but he looks and behaves like a child. He lustfully chases after Constanze in one scene, but then throws a tantrum just a few minutes later in response to the prince-archbishop's refusal to set him free. Mozart takes pride in his appearance and also could care less about it. Before coming to the emperor's place, he buys himself a fine wig. In the prince-archbishop's residence, however, he chases after Constanze and engages in other inappropriate acts without giving much thought to the fact that at any moment someone might walk in and discover them.
Moreover, Mozart is arrogant, but self-aware. Mozart attacks Salieri's work in front of the emperor and also decrees himself to be the best composer in Vienna throughout the film, yet he is conscious of his faults. As Mozart tries to convince the emperor to let him premiere an opera based on the banned play, The Marriage of Figaro, Mozart calls himself vulgar in front of the emperor. He tells the emperor that he knows that he is vulgar, but that his music is not. Mozart's self-awareness becomes more obvious in the aftermath of Leopold's death. Mozart feels tremendous guilt towards Leopold after Leopold dies. As Salieri watches Don Giovanni, Mozart's opera that premieres after Leopold's death, Salieri comments that Mozart creates a character in the opera that resembles Leopold and that this character denounces Mozart for the entire world to see.
Another contradiction is the fact that Mozart is both irresponsible and disciplined when it comes to his work. At the prince-archbishop's residence, Mozart arrives late to his performance because he was flirting with Constanze. Despite this action, however, Mozart shows his dedication to music throughout the film. Lorl, a maidservant who appears later in the film, comments on the fact that Mozart spends the majority of his days composing music. Mozart shows passion for music even in his last hours.
One last contradiction is the fact that Mozart is far from being an old man, yet he has a characteristic that is typically found in old men. Like old men, Mozart is very much living in the past. In his late twenties, Mozart is still that child that appears in the beginning of the film. Old Salieri talks about how a young Mozart travelled and performed for important individuals under the guidance of Leopold. In his late twenties, Mozart is still very dependent on his father. When he angers the prince-archbishop, Leopold is the one that apologizes to the prince-archbishop. Leopold removes the blame from Mozart and places it upon himself.
Salieri also lives in the past, but his case is a little more complex. Two versions of him are living in the past. Old Salieri, the one who is telling the narrative, feels the weight of his actions in Mozart's death even though thirty-two years have passed since Mozart died. His guilt is so strong that he tries to commit suicide and ends up instead in an asylum. The adult Salieri in old Salieri's narrative is also living in the past. Adult Salieri, who has an esteemed position in the emperor's court, is still tied to prayers he made to God as a child. Adult Mozart and adult Salieri feel entitled because of their attachment to the past. Adult Mozart always wants his way because his father has spoiled him from a very young age. Adult Salieri, on the other hand, feels that God owes him greatness because of the pact that he made with God in his childhood prayers.