Cass Anderson is driving home one dark and stormy night, taking an isolated country road, when she sees a woman sitting in a parked car. Cass stops thinking to offer her assistance but sensing that the situation may be more sinister than it appears, drives off without helping.
When she awakens the next morning, Cass learns that the woman in the car has been found murdered and that she may have unknowingly been the only witness to the crime. So what stops her from reporting what she knows to the police? Her deep mistrust of herself.
Suffering of late from short-term memory loss and anxiety, Cass’s memories are often foggy and incorrect and her mistakes regularly lead to problems with her husband and friends. As a result, Cass has learned not to trust things she sees or thinks she sees; so she keeps her information to herself.
The guilt at withholding information from the police causes Cass great stress and her memory problems begin to worsen. Soon, Cass finds herself drawn deeper and deeper into the mystery surrounding the woman’s death and she becomes increasing convinced that the murderer may be after her as well. The only problem is that no one believes that anyone is after her, only that her mental problems have become so severe that she is delusional.
As the story progresses, Cass finds herself more and more isolated and vulnerable, to the point that she alone must prove that her fears are real — that she does have information about the murder that is putting her in danger — or to accept that she has lost her mind completely.