A young woman becomes obsessed with a seemingly perfect couple she often sees at a café. When the husband is brutally murdered, she gets entangled with the widow and a mysterious man who knew the couple, leading her to question everything she thought she knew about love, death, and fate. As she delves deeper into the circumstances surrounding the husband's death, she is forced to confront unsettling truths about the nature of human relationships.

This gripping novel unfolds in the misty and myth-shrouded Baztan Valley of Navarre, Spain, where a detective returns to her hometown to investigate a series of eerie murders. The victims, teenage girls, are found in a state that suggests ritualistic killings, drawing the detective into a complex web that ties the present crimes to her own troubled past. As she delves deeper, local superstitions and family secrets emerge, challenging her rational beliefs and forcing her to confront the possibility that the answers she seeks might be as intangible as the mythical Basajaun, the invisible guardian of the forest. The story masterfully blends elements of crime, folklore, and psychological thriller, creating a suspenseful narrative that keeps the reader guessing until the very end.