Laurin is set in a small port at the turn of the last century, surrounded by a romantic river landscape with dense woods and a large castle ruin on a hill. Nine-year-old Laurin lives with her young mother Flora, her sailor father Arne, and her peculiar grandmother Olga in a remote, ivy-clad cottage in the forest.
One evening, Flora dies under mysterious circumstances, leaving Laurin feeling that something evil lurks in the village community. Two years later, Laurin's father is away at sea and she is left alone with her grandmother. The parson's son, Van Rees, returns from military service and becomes the village teacher, catching Laurin's attention with his dark and melancholy demeanor.
Laurin becomes haunted by dreams and visions, realizing that her mother and a gypsy boy were murdered by someone who frequents the castle ruin with a black wolfish dog. When her schoolfriend Stefan disappears, Laurin explores the castle ruin and discovers a trapdoor leading to a vault filled with nightmare and terror.