Inspector Amaia Salazar returns to her remote Basque hometown to hunt a ritualistic killer who targets young women in the mist-shrouded Baztan Valley. Tasked with leading the investigation, Amaia must navigate the friction between modern forensic science and the deep-seated local superstitions that haunt the region. She faces opposition from both the elusive murderer and the ghosts of her own traumatic childhood, which are inextricably linked to the valley's dark folklore. The narrative unfolds through a third-person perspective that balances the clinical demands of police work with the atmospheric tension of a landscape steeped in ancient myth.

This novel is widely recognized for its successful fusion of the police procedural genre with the eerie, atmospheric elements of regional folklore. Readers and critics frequently highlight the strength of the protagonist, Amaia Salazar, noting her depth and the psychological weight she carries throughout the investigation. The setting of the Baztan Valley is often cited as a character in its own right, providing a claustrophobic and haunting backdrop that elevates the central mystery. The narrative is praised for its ability to maintain suspense while grounding the supernatural undertones in a realistic, gritty investigative framework.