Mia, Felix Fox, and Luna Fairy discover that a magical castle has become completely invisible after losing the Crystal Prism that helps it reflect light. By using clues from movement, echoes, shadows, and rainbow reflections, they carefully navigate the unseen castle, recover the prism, and restore its colourful towers. A magical mystery that teaches observation, problem-solving, teamwork, and how using different senses and clues can help us discover what is not immediately visible.