Fourth adventure of the National Police officer Diana Dávila, this time set in Laspaúles (Huesca, Spain), a town traditionally associated with witchcraft. National Police Officer Diana Dávila is transferred to Laspaúles, a rural town in Huesca, where she must investigate, along with Chief Inspector Vázquez from the Central Unit in Madrid, the murder of a police officer, Andrés Hernández, whose death appears to be linked to witchcraft practices. The investigators discover that, before his death, the murdered officer was investigating the theft of a unique edition of Goethe's Faust, a book of great value. And, as they follow the leads, they receive anonymous messages warning them about witches and cautioning them to be wary of the town's inhabitants.