FAQ

Sixteen-year-old Rebecca (Sarah Bolger) is ecstatic about returning to Brangwyn, an exclusive girls' boarding school, and seeing her friends Charley (Valerie Tian), Dora (Melissa Farman), Sofia (Laurence Hamelin), Kiki (Gia Sandhu), and Lucy (Sarah Gadon) again. That evening, after the girls have gotten settled in, they are introduced to a new girl, Ernessa Bloch (Lily Cole), who will be assigned to a room across the hall from Rebecca's room. While Rebecca finds Ernessa eerie, Lucy and Ernessa immediately become close friends, evoking strong feelings of jealousy in Rebecca, so Rebecca immerses herself in Gothic literature, the required reading material in the class of the new English teacher, Mr Davies (Scott Speedman). As all of Rebecca's friends start falling away from her and Lucy grows weak, presumably from anorexia, Rebecca begins to suspect that Ernessa may be a modern-day Carmilla.

The Moth Diaries is a 2002 novel by American writer Rachel Klein. The novel was adapted for the movie by Canadian film-maker Mary Harron, who also directed.

Carmilla is the title character in the Gothic novella Carmilla (1872), written by Irish author Joseph Sheridan Le Fanu, predating Bram Stoker's Dracula (1897) by 25 years. The story revolves around 18-year-old Laura, who lives a lonely life in an isolated castle owned by her widowed father. When a carriage accident near the castle results in Carmilla, a young girl of Laura's age, coming to stay with them, Laura and Carmilla become close friends. When Laura's health suddenly begins to decline, it is learned that Carmilla is actually a centuries old vampire.

Having seen Ernessa going down to the basement where the students are not permitted to go, Rebecca steals a key and goes downstairs to see what Ernessa is up to. She finds a large coffinlike trunk with Ernessa's name written on it. Inside, she finds a journal written by Ernessa and dated 1907 in which Ernessa describes how she slit her own wrists following her father's suicide. Rebecca returns the book to the trunk, then writes in her own journal that she now realizes Ernessa is after her, that Ernessa wants her to die in the same manner. She returns to the basement, this time finding Ernessa sleeping in the trunk. Rebecca douses her with kerosene and sets her on fire, burning her to death. Later, as the firefighters battle the blaze, Rebecca notices the ghost of Ernessa looking at her through a hallway door. Slowly, Ernessa turns and walks down the dark hallway into the sunlight, where she disappears. Rebecca is informed that the police want to ask her some questions at the police station. In the final scene, Rebecca tosses her razor blade out the window while on her way to the station. In a voiceover, she says, They are suspicious of me, but I'm not afraid. They will find the ashes of her trunk in the basement, but they won't find a body. Ernessa is gone and she's not coming back. I set us both free.

Ernessa's true nature is left ambiguous. Some viewers think that Ernessa was supposed to be a real vampire playing with Rebecca's head, manipulating other peoples' thoughts, and draining them of their lifeforce like vampires can in some tales. However, most viewers conclude that Rebecca, still reeling from her father's suicide and Lucy's recent death, was suffering from some form of mental breakdown and that reading Carmilla put thoughts about vampires in her mind, which she then projected onto an innocent victim, Ernessa. Some viewers even wonder whether Ernessa was a real person or just a figment of Rebecca's imagination. Those who think that Ernessa was a product of Rebecca's paranoid imagination cite such evidence as Ernessa and Rebecca's lives being parallels of each another, Ernessa not being seen in any of the classes, and Ernessa only appearing to Rebecca when she's alone. Those who believe Ernessa to be real point out that other people see and interact with her, including the headmistress who introduces Ernessa to the girls at the beginning of the movie. A third group of viewers argue that Ernessa was a real student at Brangwyn but that Rebecca's unstable mind caused her to have hallucinations that involved Ernessa. Consequently, each viewer must answer the question to their own satisfaction.