When a strange new student named Ernessa (Lily Cole) befriends Lucy, Rebecca's precariously balanced world starts to teeter. Soon bizarre incidents begin happening. Distressed, Rebecca turns to her diary to share her intimate thoughts and suspicions, and to her new English teacher, Mr. Davies (Scott Speedman). Her fears heighten as the events around her eerily parallel the gothic novel Carmilla, which she is studying in class. Could Ernessa be a vampire and former guest of the old Brangwyn Hotel? When Lucy falls ill, Rebecca's determination to uncover Ernessa's secrets becomes unstoppable.