; At the beach by Mouseford Academy, Nayeon, Jisoo, Irene, Yerin and Sejeong discover a mysterious boy with blue skin washed up on the shore. He speaks an unfamiliar languange so five of them call Yoona for help. She sets them on an exciting journey to hunt for clues about the boy's origins. Could he be the prince of the underwater world of Atlantis?
3 parts