Nam-woo, an office worker, is transported back to his childhood summer after receiving a package from his friend Jun-ho. Jun-ho and Nam-woo reunite and travel to their hometown, a small fishing village, where they spend Jun-ho's last few days before he goes off to boarding school in Seoul. During their visit, Nam-woo discovers a mysterious marble and an abandoned lighthouse that transport him to a fantastical world. In this world, he meets a flying girl named Mari.