The body of a girl, the second in a month, is discovered on the banks of the Baztan River, in a gloomy and eerie setting. Is it the work of a serial killer or a creature straight out of the ancient myths?

Thirty-year-old inspector Amaia Salazar returns to her hometown, a picturesque village in the Basque Country, in a misty, rainy, forest-filled place, where myths and prejudices haunt its inhabitants. Torn between logic and the supernatural, she is forced to confront her own demons, burdened with the most challenging case she has taken on so far.