It's soon associated with the same murder one month before when the body of a teenaged girl is found on the banks of the River Baztán. Soon, rumours are flying from the local village of Elizondo. Is this the work of a ritualistic killer or could it be the basajaun, '' the'guardian' of mythology? Inspector Amaia Salazar directs the identification, taking her spine to the heart of the country where she was born, and where she expected to not return. Shrouded in freshwater and surrounded by impenetrable forests, it's a place of conflicts and also a secret from the childhood of Amaia which will keep coming back to haunt her. Faced with the village's superstitions, Amaia has to fight with the demons of her past to confront the fact of a serial killer on the loose. But as she is drawn deeper into the investigation, she feels the presence of something darker lurking within the shadows...