Mozart's next opera, Don Giovanni, is influenced by Leopold's death. Salieri goes to see this opera and admires Mozart's genius despite his continuing contempt of Mozart. Salieri sees Mozart's pain in the opera. He comments that Mozart creates a character in the opera that resembles Leopold and that this character denounces Mozart "before all the world." Despite loving the opera, Salieri's need for revenge gets the best of him, and he uses his influence to make sure that Don Giovanni is played only five times in Vienna (Salieri goes to each performance). Salieri also uses Mozart's guilt towards Leopold to torment Mozart.
Salieri purchases a costume identical to the one that Mozart bought for Leopold on Leopold's first day in Vienna. Salieri goes to Mozart's residence in the costume. Mozart is shocked when he sees a mysterious figure in the costume that Leopold once wore. He does not know that it is Salieri. Salieri, in costume, commissions Mozart to work on a Requiem. Mozart who is near financial ruins accepts the work despite the negative feelings that the masked figure instills in him.
Salieri plans on killing Mozart after Mozart completes the piece. Salieri imagines himself increasing his fame by playing the piece at Mozart's funeral and passing the piece as his own. In the present, Father Vogler gives old Salieri a horrified look. He is shocked that Salieri's younger self acted on a plan to kill Mozart.
Old Salieri continues to talk about the past. In the past, Mozart dives further into mental, physical, and financial decay. Mozart takes his wife and son to see a show that parodies Don Giovanni. Emanuel Schikaneder, an actor, is the man behind the show. Schikaneder commissions Mozart for an opera, but Constanze does not want Mozart to do the opera. She does not like how Schikaneder transforms Mozart's work into low art. Schikaneder also will not give Mozart any upfront cash for the new opera, and Constanze and Mozart are in urgent need of money.
Mozart is so desperate for money that he goes back to Michael Schlumberg's residence. In a drunken state, he begs Schlumberg for another chance to teach Schlumberg's daughter. Schlumberg tells him that the daughter is married and has long moved out of the residence. Mozart then begs Schlumberg for a loan, but Schlumberg tells him to leave. Mozart's physical and mental states further deteriorate.
Despite Constanze's warning, Mozart works on an opera for Schikaneder. Mozart works on two pieces simultaneously, one for Schikaneder and the other for the masked Salieri. Mozart feels pressure from both men. The actor visits Mozart and holds Mozart in a firm grip as he tells Mozart to finish the opera soon. Salieri's actions are not that different. Salieri forces Lorl to continue to spy on Mozart, and once he hears from Lorl that Mozart is working on a piece besides the one he hired Mozart to compose, he visits Mozart once again in costume and terrifies Mozart into focusing on the Requiem.
Constanze has a conversation with Mozart. She sees the weight of the two pieces on Mozart and urges him to focus on the one that the masked figure commissioned. She believes that the masked figure is a more reliable source of income than the actor. Mozart tells Constanze that the piece that the mask figure asks him to create is killing him. Constanze cries. She cannot understand Mozart's train of thought, and she feels helpless. She decides to stay up with Mozart as he works.
Once she falls asleep, Mozart feels the weight of Leopold's portrait that hangs near the table where he is working. He leaves the residence in the middle of the night and joins a small gathering hosted by Schikaneder. When Mozart comes back from the party, he finds that his wife and son are gone. He immediately visits his mother-in-law. Frau Weber is angry and tells Mozart that she never wanted her daughter to marry him, a statement that is false. She offers Mozart money to go to a spa and get better. Mozart does not take the money, but he is inspired by Frau Weber's rant. He sees music in Frau Weber's rant and incorporates this music into his next opera, The Magic Flute.
Salieri attends the opening of this opera. He is admiring the opera when Mozart passes out in the middle of conducting it. Mozart's state does not ruin the show. Another conductor takes over while Salieri and others usher Mozart into a carriage. In the carriage, Mozart regains consciousness, but he is too weak to go back to the opera. The carriage takes Mozart and Salieri to Mozart's residence.
Mozart and Constanze are mirror images of each other in this section of the film. They both feel completely helpless. Mozart is overwhelmed with grief and his worsening financial situation. Constanze is overwhelmed with Mozart and their worsening financial situation. They both seek escape. Mozart leaves the residence in the middle of the night and parties the night away. Constanze also leaves the residence. She goes back to her mother's place. Mozart leaving the residence in the middle of the night is the last straw for her.
Another parallel that exists between Mozart and Constanze is the love that they have for their son, Karl. Despite their troubles, Mozart and Constanze never stop being doting parents. Mozart is very kind to his son, even as his mind deteriorates. At Schikaneder's show, Mozart is happy to see Karl enjoying the performance. Moreover, just a few scenes later, Mozart checks up on his sleeping son. Constanze is as equally attached to Karl. When she leaves Mozart, she takes Karl with her. The family scenes in this section offer some lightheartedness amidst the overall bleak tone of the section.
Mozart pays for many of his past offenses in this section of the film. Michael Schlumberg, the man that Mozart walks out on in an earlier part of the film, kicks Mozart out when Mozart asks for another chance. Salieri throws Mozart's weakness (guilt towards Leopold) in Mozart's face just like Mozart kept throwing Salieri's weakness (mediocrity) in Salieri's face earlier in the film. Mozart also pays for his actions towards his father. In Don Giovanni, Mozart creates a character in his father's likeness, and this character admonishes Mozart in front of the whole world.
Mozart loses his combative spirit in this part of the film. He hides when Schikaneder comes to see how far he has progressed on the work that he was commissioned to do. Mozart is so physically and mentally frail that he relies on Constanze to protect him when Schikaneder gets violent. Mozart is humbled by his circumstances. He revisits Michael Schlumberg and begs him for a job. When Schlumberg has no job to offer him, he begs Schlumberg for a loan.
Mozart's problems seep into his music. His grief manifests itself in Don Giovanni. He has trouble finishing work. He goes on a nonsensical rant when Schikaneder asks him why he has not yet finished the opera that he was commissioned to do. Moreover, Mozart incorporates Frau Weber's rant into The Magic Flute.