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