The film is inspired by a well-documented case that has been studied by scholars and historians. The curator Juan de Miranda, Juana de los Reyes, Fray Pablo Sarmiento, Mariana the midwife and Josepha Ramos are characters based on real people. According to the official documents of the Holy Inquisition, Juana de los Reyes was not possessed by the devil but was pregnant with her own brother. She and Josepha Ramos were punished and imprisoned. Juana's brother was sent to a convent in Spain. Josepha Ramos remains in the local collective memory as an infamous colonial witch called "the mouse sucker" (la chuparratones).
The case that inspired this story occurred in 1692, the same year as the Salem Witch Trials.
To this day, Querétaro is a place where exorcisms occur on a regular basis. Recent press reports mention that there are specialized Catholic churches for this purpose that attend up to 20 cases per week.
A significant number of the crew members - including directors, writers and producers - are professors, alumni or students of the Tec de Monterrey Campus Querétaro university.
During colonial times, Querétaro was an important city because it was the border towards the northern part of the territory, where the rich silver mines were located, as well as the nomads and Chichimeca rebels, an indigenous group that resisted Spanish authority for centuries.