Narra la historia de una chica común de secundaria de 18 años que vive una experiencia profundamente misteriosa durante sus vacaciones de verano, antes de tener que regresar de golpe a la dura realidad
Ha-yeon, an ordinary second-year high school student, heads to Upo-ri with her parents for summer vacation. Struggling with friendships and family relationships, she unexpectedly meets Yu-gyeom, the young heir of a traditional Korean family. The two then experience something unbelievably mysterious.
Ha-yeon goes to Upo High School for extra classes. After sharing a special moment with Yu-gyeom, she gets angry at him for already having a girlfriend. However, Yu-gyeom continues to ask Ha-yeon to keep seeing him. The two share another special moment. When Yu-gyeom’s girlfriend, Sae-ryeong, finds out, she visits Ha-yeon late at night.
After a sudden accident, Ha-yeon leaves for Seoul, leaving behind a farewell letter. The police visit her parents and Yu-gyeom, while rumors spread at school that Sae-ryeong has died. After discovering Ha-yeon's letter, her older brother Jeong-yeon heads to Seoul to find his sister, who has become entangled with a human trafficking ring.