A year after arresting Jason Medina for the rape and murder of his step-daughter, Detective Inspector Amaia Salazar has one last duty to complete before starting her maternity leave - attending Medina's trial. When the trial is suddenly called off, Amaia is appalled. But the judge had no choice. Jason Medina has committed suicide, leaving behind a cryptic note addressed to Amaia: the single word 'Tarttalo'.

To unravel the truth behind this obscure reference to Basque mythology, Amaia must return once again to the Baztan valley, her family home and the place where she feels most vulnerable. As the investigation becomes more complicated and more personal, those closest to Amaia will be placed in mortal danger.