Spain, 1944. A group of rebels is fighting the Nazis in the mountain forests of northern Navarra. Ophelia, a 10-year-old lonely and dreamy girl, moves with her pregnant mother Carmen to the military camp of her stepfather, Captain Vidal. Vidal is an arrogant and cruel army officer, Franco, who must clear the area of rebels at all costs. Ophelia, fascinated by fairy tales, discovers an old abandoned labyrinth near the house.

The fairy takes her to the center of the maze, where she meets Faun, the owner of the dungeon. The Faun claims to know her true fate and her secret destiny. It turns out that Ophelia is the missing princess of the magic kingdom, which her father has been searching for for many centuries. Faun offers her the opportunity to return to the magical kingdom. But first, she must pass three tests before the full moon. No one should know about this.