An urban legend speaks of a girl that became lost and driven mad in the catacombs of Paris. She is known as the Shadow Girl, and will stalk and murder anyone unfortunate enough to cross her path. When the boyfriend of a famous musician is murdered on the river Seine, Marcela Novakova vows to find the elusive Shadow Girl. With the aid of the urban explorers known as the cataphiles, she will navigate the endless tunnels of the catacombs in search for Europe's most infamous murderess deep below the most romantic city in the world.