The film opens with a sadomasochistic satanic sect led by a priest who evokes the demon Aborym with a ritual. A few years later, Marco Sartori, a Roman bank employee, travels to Naples to locate his cousin Carmela, whom he hasn’t seen for years. They meet at the train station, chat at a bar, and wander through the busy streets, when four muggers snatch a precious jeweled cross from Marco that he wears around his neck. With the help of the police, Marco tries to track the thieves, but the cross has already changed hands.
The next day, Marco discovers that the girl who waited for him at the station isn’t actually his cousin, but a friend of hers, Elena, who may have fallen in love with him. Undeterred, he presses on with the search. After meeting a girl named Maria in a disco, Marco goes to a Camorra boss. The boss, knowing his line of work, offers a deal: return a list of bank accounts in exchange for the cross, but Marco refuses and is beaten by the boss’s henchmen.
The following evening, after being rescued and hosted at Maria’s house, he visits a fence named Totonno ’o Cafone in hope of locating the cross. He learns it has already been sold by Don Raffaele Esposito, a powerful Camorra boss from Somma Vesuviana. At midnight, Marco transforms into a werewolf and kills the fence. Nightmares reveal that Marco was born from a relationship between his mother and the demon Aborym, and that he is doomed to transform into a werewolf every night unless he wears the jeweled cross.
Returning to normal, Marco continues the search and reaches Don Raffaele Esposito: mistaking him for a police officer, Esposito imprisons Marco, who, after midnight, frees himself by turning into a werewolf and massacring the Camorra members. Learning that the cross is in the hands of a Roman fortune teller named Armisia, Marco heads back to Rome to recover it. When he reaches her house, he again becomes a werewolf and kills her during sexual intercourse. Thanks to Maria’s intervention, the cross is recovered and Marco regains his human appearance. Just as he holds onto the cross again, the priest from the opening scene who had evoked Aborym dies in a car accident. The film ends with Marco and Maria strolling through St. Peter’s Square, and a translucent apparition of Jesus Christ appearing to symbolize the protagonist’s newfound serenity.
