Father Rosetti is sent by the Vatican to a small city in Pennsylvania to investigate a report of an impending virgin birth, but he is attacked on the road by mysterious bikers, making him crash and leaving him catatonic.

In his place, Vatican sends Father Justin O'Carroll, not without warning him that seventy years before, the Virgin Mary appeared in an Italian village and left a message concerning the birth of a divine child at the end of the century.

After arriving in the city, O'Carroll meets a pregnant 15-year-old teen, Margaret Gallagher, who is bullied by her classmates for her claims of being a virgin.

When he returns to the Vatican, he learns that another girl claiming a virgin pregnancy, Kathleen Beavier, has surfaced in Boston, being possibly the target of a second part of the prophecy, which talks about a child of Satan.

O'Carroll finds that Kathleen's recent life mirrors exactly that of Margaret, and he is forced to investigate which girl will be the mother of which child.