Christine Lucas (Nicole Kidman) wakes up each morning in a bed she doesn’t recognise, in a house that is unfamiliar, with a man she doesn’t know. Every day her husband Ben (Colin Firth) explains that Christine was in a car accident and suffered a brain injury ten years ago which resulted in her having no memory of her life since her early twenties.
Suspicious of the life she’s living and desperate to reclaim her memory, Christine enlists the help of a neurologist, Dr Nash (Mark Strong). Dr Nash tells Christine that her memory loss occurred following a vicious attack and advises her to start documenting her day-to-day life in secret with a handheld video camera.
As Christine starts to piece together her days and missing memories she soon realises that she can’t trust anyone, especially her husband Ben.