"El padre de Cain" tells the story of Eloy, a lieutenant in the Civil Guard who is obsessed with the war on terrorism. A democrat and adventurer, for his first post, Eloy volunteers to be assigned to the Intxaurrondo Barracks in the troubled city of San Sebastián, where assaults with machine guns, point-blank shootings and mortar attacks are a constant. Shortly before the attempted coup in the early 80's, Eloy leaves his young wife in Madrid in order to confront persecution by "abertzales" and the violence of ETA.

Nevertheless, amid this atmosphere of terror and fear, he also discovers an Euskadi that is mostly peaceful and a side of San Sebastián that is welcoming, where love becomes another protagonist in an thrilling story with a surprising outcome. An unexpected love will radically change his life forever.