At Ottavia's trial in the basilica of Pompeii, she protests her innocence. Although Appio, Pubblio, and Clodio's testimony is damning, Sallustio is still reluctant to find her guilty. At this point, ominous rumbling is heard from Mount Vesuvius, which is taken by the augurs as a sign that the gods are displeased with Sallustio's hesitation. Ottavia is thus condemned to be buried alive. As she is led into the tomb, accompanied by her faithful handmaidens, Ottavia turns to her husband one last time, swears her innocence, and entrusts their young son, Menenio, to his care. At this point, Vesuvius erupts with a tremendous explosion. Sallustio now takes this as a sign that a terrible injustice is about to be done and halts the execution. Pubblio, believing that his perfidy has brought disaster to Pompeii, confesses all and names Appio as the instigator of the plot. He and Appio are sealed in the tomb instead of Ottavia. As boulders and ash rain down on the city and all flee in panic, Menenio arrives with a chariot and rescues his parents. The eruption becomes ever stronger and the sky is filled with fire and lightning. The curtain falls on a scene of desolation.