Marnie Logan often feels like she's being watched: a warm breath on the back of her neck, or a shadow in the corner of her eye that vanishes when she turns her head.

She has reason to be frightened. Her husband Daniel has inexplicably vanished, and the police have no leads in the case. Without proof of death or evidence of foul play, she can't access his bank accounts or his life insurance. Depressed and increasingly desperate, she seeks the help of clinical psychologist Joe O'Loughlin.

O'Loughlin is concerned by Marnie's reluctance to talk about the past and anxious to uncover what Marnie is withholding that could help with her treatment. The breakthrough in Marnie's therapy and Daniel's disappearance arrives when Marnie shares with O'Loughlin her discovery of the Big Red Book, a collage of pictures, interviews, and anecdotes from Marnie's friends and relatives that Daniel had been compiling as part of a surprise birthday gift.

Daniel's explorations into Marnie's past led him to a shocking revelation on the eve of his disappearance: Anyone who has ever gotten close to Marnie has paid an exacting price. A cold-blooded killer is eliminating the people in Marnie's life, and now that O'Laughlin is a part of it, he is next in line.