Ever since a vicious attack nearly claimed her life, Christine Lucas (Nicole Kidman) has suffered from anterograde amnesia and is unable to form new memories. Every morning, she becomes reacquainted with her husband, Ben (Colin Firth), and the other constants in her life. In accordance with her doctor's (Mark Strong) instructions, Christine keeps a video diary. As Christine starts to uncover terrifying truths about her past, she begins to question everything -- and everyone -- around her.