At the back of her grandmother's closet lies a mystery. After her grandmother's death, Eva finds a series of diaries detailing the life of a girl caught up in the magic of the Roaring Twenties. She cannot reconcile the young woman in these diaries with the miserable old woman she loved so fiercely. What happened to change her grandmother so drastically? Eva is desperate to know more about this period in her grandmother's life. What is the light of the world, and who is the mysterious girl that her grandmother fell in love with? Eva starts to investigate the puzzle her grandmother left behind. With the help of a local historian and his enigmatic assistant Olivia, they find a forgotten labyrinth under the city streets. But they are not the only ones down there. Someone else is searching for the light of the world.