Yoko Mizutani, a nurse at Kikumisaka Hospital, a general hospital, is frightened by a series of bizarre incidents that occur at the hospital. One night, a boy in the psychiatric department goes missing, and when the nurses on duty search the hospital, they find him standing in the mortuary holding a skull. The police investigate the skull and find that it is the skull of the former deputy director, who had gone missing with his mistress. The mistress of the former deputy director was Etsuko Mizutani, Yoko's older sister....