At an exclusive girls' boarding school, a sixteen-year-old girl records her most intimate thoughts in a diary. The object of her obsession is her room-mate, Lucy Blake, and Lucy's friendship with their new and disturbing classmate. Ernessa is a mysterious presence with pale skin and hypnotic eyes. Around her swirl dark secrets and a series of ominous disasters. As fear spreads through the school, fantasy and reality mingle into a waking nightmare of gothic menace, fuelled by the lusts and fears of adolescence.

And at the centre of the diary is the question that haunts all who read it: Is Ernessa really a vampire? Or is the narrator trapped in her own fevered imagination?