Once again, Harvard professor of religion and archaeology Cal Donovan has been summoned by Pope Celestine to investigate a seemingly impossible miracle. Three Catholic teenage girls, from different corners of the world, have fallen pregnant. All three girls are named Mary and all three girls have been proven to be virgins. Are they really all bearing the son of God?
Before Cal has a chance to visit all three girls, one of the Marys disappears … and then another. As he struggles to uncover the truth, Cal realizes that much more than his own and others’ lives are at stake: could this apparent miracle really cause the collapse of the Catholic faith?