This is what the police know: English teacher Clare Cassidy's friend Ella has just been murdered. Clare and Ella had recently fallen out.

Found beside the body was a line from The Stranger, a story by the Gothic writer Clare teaches, and the murder scene is identical to one of the deaths in the story. This is what Clare knows: No one else was aware of her fight with Ella. Few others have even read The Stranger.

Someone has wormed their way into her life and her work. They know her darkest secrets. And they don't mean well.

This is what the killer knows: Who will be next to die.