Battista seeks out the help of a Benandanti witch, Vulnavia, because his wife, Donna, has had six stillborn girls, and she’s pregnant with her seventh child. Vulnavia, who communicates through telepathy and travels with a white wolfhound familiar, agrees to help him when she hears that it would be the seventh daughter of a seventh daughter.
But Vulnavia’s offer of assistance is not without cost. Vulnavia is a centenarian witch reaching the end of her life, and she must set out to find her replacement: a seventh daughter of a seventh daughter born with a caul. Vulnavia agrees to help ensure that Donna’s seventh pregnancy will be successful, under one condition: Battista must sacrifice himself by walking into the ocean during a full moon on the night of his daughter Caterina's birth to give the child the gift of the caul.
Thirteen years later, as a mute Caterina is on the cusp of womanhood, Donna notices changes in her daughter’s behavior that have her worried, including suspicions of her involvement in the death of their cat, Victoria. Meanwhile, newly malevolent members of the community of Friuli, a Californian sister town to the Italian city, are trying to convince Donna that Caterina is possessed by an evil force.
Donna begins piecing together the circumstances of the night of Caterina’s birth and Battista’s sacrifice while researching demonic rituals in dusty libraries. As Donna fears Caterina will be taken by the increasingly powerful forces of evil taking hold of their town, she must decide how best to help her daughter.
Donna is convinced by the townspeople of Friuli that Caterina must be killed to save her soul and their town.
She must figure out that Caterina is a force of good and help Caterina rise to her fated purpose before Vulnavia’s powers fail completely. She succeeds and the people of Friuli are freed of the evil force possessing them.
Donna mourns the loss of her daughter from her life, while always knowing that Caterina is watching over and protecting her. Battista returns from the ocean, his sacrifice a success, and they are reunited.