Set in Seoul in 1938 during the Korea under Japanese rule, the film centers on Ju-ran (Park Boyoung), a sickly young girl who gets transferred to a sanatorium/girls' boarding school to recover her health. Her physical condition improves thanks to her new friend Yeon-deok, and the headmistress's special treatment program. But she soon notices that students are disappearing one by one and that her own body is undergoing abnormal changes. Determined to uncover the truth, Ju-ran starts to investigate the mysterious happenings and the school's possible role in them.