When Min-Ah discovers a shared diary, she is soon fascinated to discover that two girls she assumed were little more than close friends, were engaged in a much closer, forbidden relationship. As she reads on, she is unable to tear her eyes away from the high drama of her classmates' lives as the allure of the secret diary begins to take over. When one of the diary's writers is found dead from an apparent suicide, rumours spread and Min-Ah begins to feel a strange presence. The once-tranquil school is transformed into a place of morbid terror, as the words written in the journal, "memento mori" (remember the dead), come to life...