Rebecca (Sarah Bolger), a young girl, her father's suicide troubled, her travels in an elite girls boarding school. Soon, the popular and sunny Lucy (Sarah Gadon), and her sense of security and Rebecca's close friendship the coming of the dark and mysterious Ernessa (Lily Cole) to break. Soon, Lucy should Ernessa beautiful magic, emotional and physical consumption through their strong friendship. Rebecca, her sorrow and Lucy's refusal of friendship, affection, lost and confused. She quickly became a crush on her pretty English teacher, Mr. Davis (Scott Speedman), immersed in their own gothic - vampire novel Carmilla his lesson theme developed. Rebecca began to doubt Ernessa is a vampire, but in spite of the suspicious deaths begin to lose weight and Lucy, her fear was a simple girl jealous treatment. Accumulation as a young girl's body, the line between reality and fantasy begins to fade, Rebecca decided to take action and get rid of Ernessa.