The narrative of Amadeus is framed by the confession of an elderly Antonio Salieri in a mental asylum, who dramatically claims to a priest, "I killed Mozart." The film then unfolds as an extended flashback, detailing how Salieri, once Vienna's most respected composer, orchestrated the demise of his brilliant rival. Salieri recognizes Mozart's genius as the voice of God, a gift he himself prayed for but was denied. Believing God is mocking him through Mozart's vulgarity, Salieri renounces his faith and vows to destroy Mozart as a means of taking revenge on God.
Salieri's plot is one of slow, psychological torment. He uses his influence at court to block Mozart's appointments and have his operas cancelled. The key turning point comes after the death of Mozart's stern father, Leopold. Sensing Mozart's deep-seated guilt and fear regarding his father, Salieri concocts his master plan. He disguises himself in a menacing mask and costume that Leopold once wore and commissions Mozart to write a Requiem Mass, a mass for the dead. The unstable Mozart, overworked and drinking heavily, believes he is being haunted by his father's ghost, commissioning a requiem for himself.
In the film's climax, a deathly ill Mozart collapses while conducting 'The Magic Flute'. Salieri takes him home and, seeing his chance to steal the Requiem, offers to help him finish it. This leads to the iconic deathbed dictation scene, where a feverish Mozart dictates the final passages of the 'Confutatis' to an astonished Salieri, who is simultaneously helping and destroying his idol. Before Salieri can claim the finished work, Mozart's wife Constanze returns, locks the manuscript away, and discovers Mozart has died from exhaustion. Due to his debts, Mozart is unceremoniously dumped into a pauper's mass grave in the rain.
The ending reveals the tragic irony of Salieri's life. He tells the priest that God chose to destroy His beloved Mozart rather than let Salieri share in a shred of his glory. Salieri outlived Mozart by decades, but was forced to watch his own fame fade while Mozart's grew into legend. His 'victory' was to be left alive, forgotten, and tormented by his own mediocrity. His confession is not one of literal murder, but of a spiritual assassination driven by envy. His final act in the asylum is to 'absolve' his fellow mediocrities, embracing his delusion that he is a figure of historical importance—the patron saint of the ungifted.