When DCI Guillermo Downes is called to the scene of a murder, he realizes the victim is well known to him. A decade earlier, Downes made a promise to the families of two missing girls that he would find their daughters. Although cleared, the dead man had been a suspect in their disappearance. And yet his death seems to offer fresh hope that the detective will finally make good on his promise. But as Downes, forced to flee his Argentinian homeland as a young man, and tormented by his own troubled past, pursues the case alongside a new partner, Sergeant Graves, it soon becomes clear to them both that there's a darkness at the heart of the investigation more dreadful than either could ever have imagined.