We see Salieri, a great composer of his time, at an old age. The Venticello on either side as we hear the exposition of the play "Amadeus". The play is told in flashback through Salieri's point of view.
Salieri's first run in with Mozart. Mozart is fooling around with Costanze and he is mortified by their childish behavior. Then Mozart leaves to perform the Adagio of Serenade for Thirteen Wind Instruments and Salieri is amazed by his talent... and jealous.
MOZART... spiteful, sniggering, conceited, infantine Mozart! The Creature must be destroyed.
Mozart plays Salieri's march completely by memory, and adds The Marriage of Figaro making a fool out of Salieri... was this his first thought to murder Mozart?
Constanze tells Salieri they have no money, and their reputation is going downhill fast. She agrees to bring Mozart's portfolio behind his back, and has secret meetings with Salieri in order to help Mozart.
Salierirealizes his fate in all this looking at Mozart's manuscripts. His envy rises and takes over him. He makes Mozart an enemy, but always keeps him close...
Salieri as an old man is in the last hour of his life, and tells us he does not wish for forgiveness. He had a terrifying purpose, and Mozart was the battleground.