The Unknown, a magical land teeming with blue fireflies, and Refugia, a highly-controlled city completely walled off from magic. One day inquisitive girls from Refugia discover a mysterious old book and a red necklace in a library. Without knowing what is in their possession, they curiously follow the blue fireflies out of the city, crossing barriers that no one has ever crossed before. With the help of the legendary Crimson Heart and a mysterious message, "Break the curse of Blue Firefly Island," they venture deeper into the Unknown uncovering the secret of Refugia and the truth behind the blue fireflies. What lies ahead for the girls from Refugia?Crimson Heart (HYBE)