The female diver, Somyeong, has an unexpected encounter with Yeo-Hae, a merman, in the depths of the sea. While wielding a sickle, she accidentally strikes him. In the chaos, Somyeong loses consciousness, only to later awaken and discover that Yeo-Hae, despite the injury, had saved her life. Stricken with guilt for causing him harm, Somyeong...