Pisa, 11th century. Spina, a young priestess daughter of Peter, is devoted to keeping a flame burning that illuminates the way back for those returning from the Crusade. But the Florentine knight Lamberto falls in love with her and the two young men fail in the vow of chastity that Spina committed. The shame for having betrayed the promise of purity made pushes Spina to suicide and Lamberto kills himself with her.
Well-respected Pompeiian Glaucus performs an act of kindness by purchasing Nydia, a blind slave being mistreated by her owner. Nydia falls in love with her new master, but he only has eyes for Ione. Ione in turn is lusted after by Arbace, an Egyptian high priest of Isis. When Nydia beseeches Isis for help in capturing Glaucus' heart, Arbace gives her a "love" potion-- an elixir made to drive Glaucus mad, securing Ione for himself. Ultimately, Mount Vesuvius will end their lives and seal their fates in a terrible, glorious eruption.
This story first takes you to Misslimeri, a little Sicilian village, and into the home of Don Ruggero, a wealthy landowner. Don Ruggero is an iron-hearted man and strongly prejudiced against the lower classes. His son, Corrado, a young fellow, loves Rosalia, a shepherdess, but Don Ruggero has always refused to allow their marriage and to recognize little Vincenzino, their child, as his grandchild. Finally to destroy all Corrado's hopes, he discharges poor Rosalia from his farm, where she had been employed for many years. Even the sight of her departure with Vincenzino in her arms does not soften him. Rosalia is the very ideal of the Sicilian beauty, and Capt. Altieri, an officer in the service of the Dominators, the Bourbons, admires her immensely, but all his approaches are strongly repulsed by her. Don Ruggero and his son have for a long time conspired to free their motherland from the hands of the Bourbons, and when they receive news of the arrival of Garibaldi.
