Annoyed by the rumors about her involvement in the death of a fellow student, Jung Soo-jin is determined to clear things up and regain the trust of her beloved Jang Sung-tae. But as the couple searches for evidence, they learn about a much darker secret deep within the school's depths and become prey in a relentless hunt.

At the same time, former trainee teacher Kang Seo-yeon arrives to investigate the ambiguous circumstances surrounding her father's death at the school. Relying on her knowledge of the occult, Seo-yeon attempts to reverse an ancient ritual while avoiding a powerful and malevolent ghost that relentlessly draws her in.

Having made a promise that cannot be broken, freshman Yoo Ji-min seeks a way to bring peace to the restless spirit of Han Na-young. Delving into the school's tragic history and the complex relationships among its students, Ji-min makes a fateful discovery that will lift the veil of obscurity once and for all.