Nueva España (present-day Mexico), 1798. Friar Dionisio de Fuensalida, a monk and the chaplain of the Brotherhood of the Knights of Saint Michael, has finished translating a handbook on vampirism and supernatural creatures of the night by Dr. Marinescu, a European expert. Dionisio sends Marinescu a
copy of the book in Spanish to let him know the work is done but Marinescu will not be the only person to read the new translation.
Sister Filotea del Niño Jesús, a nun who is cloistered in La Enseñanza convent (built by her family), receives a visit from friar Dionisio. It appears that he is there to pick up a food delivery for the inquisitor, however, what he wants is to share a fragment of Marinescu’s manuscript in Spanish with Sister
As soon as Dionisio and the nun can speak privately, the friar informs her about a series of murders of important men. Since all the corpses were found with two marks on their necks and no weapons in their pockets, Dionisio thinks that a vampire is the culprit. Filotea, on the other hand, is more skeptical and insists that the victims may have been killed with a sharp, thin weapon. Sister Filotea keeps the copy of the book on vampires to study more closely. She has always been interested in more than praying and convent chores. Will the friar and the nun work together to reveal who the murderer is?