When Detective Inspector Amaia Salazar is called in to investigate the death of a baby girl, she finds a suspicious mark across the child's face - an ominous sign that points to murder. The baby's father was caught trying to run away with the body, whether from guilt or grief nobody can be sure. And when the girl's grandmother tells the police that the 'Inguma' was responsible - an evil demon of Basque mythology that kills people in their sleep - Amaia is forced to return to the Baztan valley for answers. Back where it all began, in the depths of a blizzard, she comes face to face with a ghost from her past. And finally uncovers a devastating truth that has ravaged the valley for years.