The exposition comes fast, fast, fast here. Two minutes in and we know this: after suffering a debilitating brain injury, Catherine (Nicole Kidman) goes from one day to the next knowing nothing about her past life. Nothing even about her husband Ben (Colin Firth), who is forced to recount her life-story each and every morning while she looks on, dazed and confused.
Then we learn Catherine has been seeking treatment for her crippling amnesia from neuropsychologist Dr Nash (Mark Strong). He's been treating Catherine with various techniques, including the use of a video diary so she can remember what she was thinking the day before. And he's being doing it without Ben's knowledge. The intervention is working – it's bringing up scattered shards of Catherine's past and the attack that sentenced her to a life lived in the dark.
Problem is, some of the memories contradict what Ben has been saying and when questioned about this he becomes bizarrely evasive. Soon after Catherine begins to examine more closely Dr Nash's treatment and his motives. Relentlessly unsure, Catherine finds herself trapped between memories, stories and ultimately, two men.
Based on the best-selling British novel by SJ Watson, Before I Go to Sleep is directed by Rowan Joffe. It asks a lot of the main characters (the cast is essentially three), and Kidman, Firth and Strong deliver admirably. The limited cast, narrow view of the outside world, and cold, bleak locations add a veneer of isolation to everything, and thrusts you right into the middle of Catherine's terrible dilemma.
Which is not to say that some of the contrivances border on the preposterous. It's best not to deeply examine all the plot points or search for realism where there isn't any. Before I Go to Sleep works best when you get lost in the suspense, and not the psychological stuff. For the most part, the film is a pleasant diversion, and if you can free yourself from digging too deep and can get caught up in Catherine's lonely world, and her quest to free herself from it, the ride is one worth taking.