In the prehistoric deposit of Atapuerca (Burgos, in Castile and León; northwestern to Spain), the corpse of a young girl, Eva Santos, is found following an ancient ritual in the same way that another girl was found, Teresa Yaner, six years ago. The similarities with the previous murder leads the judge to reunite the two homicide detectives who investigated the first case hoping that their knowledge about the killer get the arrest that previously they couldn't. They are Silvia Guzmán and Daniel Velarde, who during the first investigation lived a passionate romance but the failed attempt to close the case catching the main suspect, Carlos Béjar, did that she continues traumatized with it, while he's asked a leave of absence from the police department to work as private security for the president of a powerful oil company. With Silvia leading the investigation and Daniel hired as external adviser, they two are forced to put their difference apart if they want get the result that the judge ordered them. But according the investigation begins, Silvia and Daniel find not only that Eva isn't the innocent girl that she seemed, but she was involved with a young group obsessed with the prehistory and the wild lifestyle with no moral of the hominids. Convinced that Béjar have returned to his bad habits, Silvia and Daniel must work against the clock to prove her theory before more corpses be found.