A knock at the door. Two monks from the order of Santa Reparta have arrived. They've come for the money that they heard he left them. They are shocked to find that Buoso's will has only allotted five lire for their order. Gianni Schicchi gives them their five lire and shoves them out of the door. Gianni Schicchi pictures the relatives poisoning Buoso. He thinks he hears the relatives coming for revenge and he writes something on a piece of parchment and stuffs it in the dead Buoso's shirt.
The family enters. They threaten Gianni Schicchi and call him a murderer. Schicchi begs for mercy. They are about to attack him when the Bargello arrives. The relatives pretend to mourn for their poor dead Buoso. They all accuse Gianni Schicchi of killing Buoso for the inheritance he gained. Schicchi claims he is innocent. One by one he discreetly tells the relatives that he knows about the poisoned food that they each brought to Buoso. While the Bargello makes the prepared speech about why he's there, all of the relatives grovel at Gianni Schicchi's feet telling him that they love him and that the other relatives hate him. They all ask for his help and promise rewards if he helps them.
The Bargello is determined to discover how Buoso died. He declares that the guilty party will be punished . He tells Simone that if he has an accusation against Gianni Schicchi to go ahead and make it. Simone withdraws his accusation in fear of Gianni Schicchi. Bargello then does his duty and accuses Gianni Schicchi of the crime. Schicchi claims his innocence and says he knows what really happened. All of the relatives offer Gianni Schicchi the inheritances they have recently gained if he will save them.
Gianni Schicchi goes on to explain that he heard from Pinellino that Buoso had written a will and that Gianni Schicchi was in it. He says he ran to the house to thank Buoso for his kindness and to offer any help he could give. He says that the relatives were all there and that they were gathered around Buoso. They were not happy to see him at all. Gianni Schicchi claims that they were jealous of the large inheritance he was to receive upon Buoso's death. He continues, commenting on how he expected to see the relatives mourning but instead Buoso was sitting up in his bed and enjoying a feast brought to him by his relatives. Then Buoso began to shake and he cried out. Just before he died, says Gianni Schicchi, he whispered, " May God forgive me."
"Poor Buoso, you were poisoned!" exclaims Gianni Schicchi. The relatives question each other nervously. "What has he done?" Gianni Schicchi walks over and weeps on Buoso's dead body. He "discovers" the note that he stuffed in Buoso's shirt earlier. He reads it aloud: I, Buoso Donati, have chosen to take my life by poison. May God forgive me.
The Magistrate says it is enough proof for him. He takes the will and the note and leaves. The relatives realize that they've been tricked again by Gianni Schicchi. Now they all have to give up their inheritances. Then, one of them brings up the point that Lauretta and Rinuccio are getting married. And, since Lauretta is Gianni Schicchi's only child, they would get everything if Gianni Schicchi were to die.
The relatives approach Gianni Schicchi planning to kill him when suddenly-- A lightning bolt! Schicchi blows out a candle. In the dark, the sheet on Buoso's bed seems to rise. A voice is heard: "I am the ghost of Buoso Donati. Curse upon you all! Leave! Leave before I rise from the dead and haunt you!" All of the relatives but Zita run from the house screaming. She remains cowering on the floor. "I've lost everything," she says. "I hate you Gianni Schicchi!"
Schicchi remarks that he too is lonely. "What is life without love?" he asks. He then offers Zita some wine. She reminds him that it's poisoned and goes down to the cellar for some good wine. Gianni Schicchi addresses the audience: "Ladies and Gentlemen, the upstart composer has dared show his face on the same evening as the great Puccini. Let us send him to hell or grant him, like me, Extenuating Circumstances."