A killer at large in a remote Basque Country valley , a detective to rival Sarah Lund, myth versus reality, masterful storytelling -- the Spanish bestseller that has taken Europe by storm.

The naked body of a teenage girl is found on the banks of the River Baztán. Less than 24 hours after this discovery, a link is made to the murder of another girl the month before. Is this the work of a ritualistic killer or of the Invisible Guardian, the Basajaun, a creature of Basque mythology?

30-year-old Inspector Amaia Salazar heads an investigation which will take her back to Elizondo, the village in the heart of Basque country where she was born, and to which she had hoped never to return. A place of mists, rain and forests. A place of unresolved conflicts, of a dark secret that scarred her childhood and which will come back to torment her.

Torn between the rational, procedural part of her job and local myths and superstitions, Amaia Salazar has to fight off the demons of her past in order to confront the reality of a serial killer at loose in a region steeped in the history of the Spanish Inquisition.