The female diver, Somyeong, has an unexpected encounter with Yeohae, 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 Yeohae, despite the injury, had saved her life. Stricken with guilt for causing him harm, Somyeong decides to bring the injured merman back to her home, hoping to tend to his wounds and make amends. However, as she begins to treat him, she finds herself swept up in Yeohae's rut. What started as a rescue soon transforms into an unexpected and irresistible encounter.