Fifteen-year-old Oscar Drai meets the strange Marina while he’s exploring an old quarter of Barcelona. She leads Oscar to a cemetery, where they watch a macabre ritual that occurs on the last Sunday of each month. At exactly ten o’clock in the morning, a woman shrouded in a black velvet cloak descends from her carriage to place a single rose on an unmarked grave.

When Oscar and Marina decide to follow her, they begin a journey that transports them to a forgotten postwar Barcelona–a world of aristocrats and actresses, inventors and tycoons–an reveals a dark secret that lies waiting in the mysterious labyrinth beneath the city streets.