A wealthy real estate developer named Liu Xuan buys the Green Gulf, a pristine coastal area, for a new business venture. Unbeknownst to him, the land is an important habitat for marine life, including a hidden community of mermaids. To protect their home from destruction due to Liu's industrial plans and pollution, the mermaids devise a plan to stop him. They send Shan, a beautiful young mermaid who can transform into human form, to seduce and assassinate Liu. She integrates herself into his life, finding opportunities to get close to him under the guise of an ordinary woman.

As Shan spends more time with Liu Xuan, she discovers a more humane side to his otherwise ruthless business persona. Her initial intentions become conflicted as she starts to develop real feelings for him. Liu also becomes increasingly curious and fond of Shan, unaware of her true identity and mission. This budding relationship sets off a series of unforeseen events that challenge both Shan's loyalty to her mermaid kin and Liu's commitment to his development project. As complications escalate and truths are unveiled, both characters find themselves at a crucial crossroads that will determine the fate of their worlds.