In the first year of King Sunjo's reign, Ding Ruoquan (played by Seol Kyung-gu) was exiled to the remote Heishan Island due to the persecution incident during the Xinyou reign. After arriving on the island, Ding Ruoquan developed a strong interest in the marine life here and decided to write a book about marine life. He sought help from Changda (played by Byeon Yo-han), a young fisherman who was born and raised here and familiar with various marine life, but Changda initially refused because Ding Ruoquan was a criminal. Later, Ding Ruoquan learned that Changda often encountered difficulties in the process of self-study literacy, so he proposed to teach each other the knowledge they were good at. Changda finally agreed, and the two became each other's mentors and friends in the collision. However, Ding Ruoquan was disappointed when he learned that Changda's purpose of studying was to pursue a career in officialdom. Changda also understood that the two had their own ambitions, and the two, who were both teachers and friends, decided to go their separate ways...