After Mozart's first performance of Figaro for the Emperor, he speaks with Salieri for reassurance of his great work. Far more different than anything ever done before... the best opera ever written.
Mozart and Costanze become very poor, she is pregnant and Mozart's father won't provide anything for them. Salieri hears of Mozart's strange dreams of a looming figure... he is also a part of the Masons now, receiving money from them.
Salieri offers to help Mozart, but he refuses because he is writing a piece about the brotherly love of the Masons. He plotted his own destruction with this opera, and Salieri never told him... the Masons disowned him.
Costanze has left Mozart, and he still has this dream of a silhouette that came to him last night. It old him to write a Requiem mass... for himself. It must be completed when he sees him next... Salieri sees his plans unfolding, and he didn't have to do a thing!
Salieri finds a terribly sick Mozart writing the Requiem he spoke about earlier. Mozart has gone insane writing this piece and is dying. His wife has left him, and he has nothing but his last Requiem.
Costanze finally comes back, remarried and she talks Mozart to death. He is composing the last of hisRequiem in his head as Costanze realizes he is dead. His requiem was never finished.