"We all have a secret buried under lock and key in the attic of our soul. This is mine."

When 15-year-old Oscar Drai suddenly vanishes from his boarding school in Barcelona, no one knows his whereabouts for seven days and seven nights.

His story begins when he meets the strange Marina while he's exploring an old quarter of the city. She leads Oscar to a cemetery, where they watch a macabre ritual that occurs on the last Sunday of each month. At exactly 10:00 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.