Christine (Nicole Kidman) wakes up every morning remembering nothing. Gradually, she pieces things together. Her walls are plastered with photos of her wedding day to help her remember that she is married to Ben (Colin Firth), the man she finds lying next to her in bed. Every drawer is labelled to help her find her clothes and downstairs is a list of her allergies, hobbies and interests. She spends her days working out who she is and simply passing the time until she goes back to sleep and forgets the day’s events all over again.
Her condition is a result of a traumatic accident that she suffered fourteen years ago and which, of course, she cannot remember. Unbeknown to Ben, she has begun a course of treatment with Dr Nash (Mark Strong) in an attempt to help her recall what really happened. He encourages her to keep a video diary of her daily experiences and soon she is beginning to question everything around her. Can she really trust the secretive Dr Nash? What about Ben, who claims to keep certain things hidden from her for the good of their marriage? Or are her concerns simply the products of a paranoid mind?