In May 1980, fifteen-year-old Oscar Drai vanishes from his boarding school in Barcelona. For seven days and nichts, no one knows his whereabouts... His story begins when he meets the mysterious Marina, the daughter of a reclusive painter. She takes him to a graveyard where they witness a macabre ritual. On the last Sunday of every month, a woman shrouded in black walks over to a gravestone that bears no name, only the emblem of a black butterfly... When Oscar and Marina decide to follow her, they begin a journey that takes them to the heart of a forgotten, post-war Barcelona. Beneath the streets a dark secret lies waiting...