Ich. Darf. Nicht. Schlafen.

Literally messing with your head, Nicole Kidman plays a woman who suffered Trauma to the head that makes her forget the past 15 years of her life when she falls asleep. She wakes up next to her husband, a man she does not know unforgettably played by Colin Firth, and as her doctor played by Mark Strong begins to help her deal with the illness things about her past begin to burst out like a kid taking out puzzle pieces and some how she has to put this puzzle together, even though when she wakes in the morning, the puzzle's messed up again. It's a strange mystery watching the protagonist solve the mystery that is her life. The whole thing would have come off one dimensional if it were not for Colin Firth's part as the emotionally distress husband who loves his wife but wants somethings to stay lost in her memory. It was an enjoyable ride watching the mystery unfold, definitely glad I saw it.

In a very real way, our memories are who we are - our identities as individuals depend in an almost terrifying way upon our ability to remember what we do (and what we've done), why we do it, and whom we love. That's why the notion of memory-making (and losing) looms so very large in the art we create. In the cinematic realm alone, characters whose memories are sorely compromised have starred in thrillers (Memento), romantic comedies (50 First Dates) and weepies (The Notebook). Before I Go To Sleep, based on the novel by S.J. Watson, is a chilling if not entirely effective blend of family drama and thriller, trading on the heartache and horror that comes with losing oneself every single day.

Christine (Nicole Kidman) wakes up every morning with no memory of the last fifteen years of her life. Ben (Colin Firth), the stranger who shares her life and bed, informs her that he is her husband and that she lost her ability to make new memories after a bad car accident several years ago. Any attempt to forge lasting memories seems futile - and yet, Christine tries. She receives a phone call from Dr. Nasch (Mark Strong), a neurologist who assures her that they've been working to improve her condition. He reminds her that she's been keeping a video diary every day: one that, upon review, suggests that Ben is not telling her the whole truth about their shared life and history.

It's to writer-director Rowan Joffe's credit that he mostly manages to make a very personal - and inevitably repetitive - journey of discovery both cinematic and chilling. As Christine awakes each day with her memory reset, Joffe finds inventive and intriguing ways to ramp up the spinetingling alienation she feels from her own life and husband. He captures Christine's terror, doubt and paranoia in the shuddery footage she takes of herself while hidden away in the bathroom from a husband she doesn't recognise. As the wheels within the narrative spin and turn, Joffe's camera makes villains and heroes out of everybody: Ben, in particular, shifts from one to the other on an almost daily basis, as Christine doubts and then trusts the love this man must have for her to stay by her side for so many years.

Unfortunately, Joffe can't quite sustain the tension throughout - the film sags noticeably in parts, as Christine flounders miserably between very few choices. There are many twists, as she uncovers people and secrets in her past that will inevitably disappear from her grasp within a day, including a final doozy of a revelation. But Joffe winds up wasting much of this tension and intrigue with an oddly definitive ending. In a film filled with questions, doubts and uncertainties, it feels completely out of place and emotionally untrue.

Joffe's cast, at least, is unreservedly excellent. Kidman delivers her most fascinating performance in ages, one that's equal parts vulnerable and strong. Her Christine is very much a victim of her circumstances - and possibly her husband - but Kidman skilfully imbues her with a steely determination to reclaim her life and identity against very poor odds. Firth, too, is fantastic, shading both light and darkness into his trademark charm - enough to make us believe that he's the kind of man who could love and/or betray Christine with all of his heart.

It's a shame, then, that the final frames of the film don't live up to its promise or potential. Joffe has hit upon something truly unnerving with his premise: Christine's condition provides the ideal backdrop for either the perfect crime, or a love story for the ages. Before I Go To Sleep quite effectively teeters between the two extremes, as does Christine, but ultimately fails to follow through when the true depths of its darkness are revealed.

In 1995, there was a movie called "While You Were Sleeping", a romantic vehicle for Sandra Bullock, but this 2014 similarly-titled work is very different: a thriller with Nicole Kidman in the central role as Christine, a woman who suffered a serious assault years ago and now forgets everything each time she sleeps. Two men are trying to help her, husband Ben (Colin Firth) and therapist Dr Nash (Mark Strong). Like most standard thrillers, we find that our assessments of the principals swing back and forth before 'the big reveal'.

There is a sub-genre of movies involving limited memory - think "Blink", "The Bourne Identity" or "50 First Dates" to name just a few - and "Before I Go To Sleep" is not the best of them (that would be "Memento") but, if one does not think too much about the implausible narrative, this is entertaining enough, helped by good source material (the best-selling novel by S J Watson) and the solid acting (Kidman with a good English accent, Firth not as straighforwardly charming as he is usually, Strong not as as unremittingly threatening as he is so often).

I agree with the reviewer who wrote that this was "three quarters of a very good film." The cast is marvelous. Kidman brings movie queen presence and guarded vulnerability to her role, as only she can. The icy, remote, sparse atmosphere of the film is noteworthy, but somehow creates a detachment from the raw emotions of the story. The plot unfolds in an efficient, generally satisfying manner. However, the film is sober, where it should have been flamboyant, and safe where it might have been edgy. In the end, I was wishing this had been filmed with panache, by a stylish and adventurous director. Atmosphere and character developments might have been richer and more complex. As it stands, it is a solid, classy, well-acted potboiler.

Overview: Clever, emotional, Kidman in her 40's is a totally different actress (hopefully she'll get a role that will become a classic).

If you've seen 50 First Dates and Momento then you will have this movie pretty much figured out in the first 15 minutes or so. However that said it still manages to leave you just as uncertain about what's going on along with Kidman's character until the reveal. Careful observation will give you the clues though. The plot is clever and as you'd expect Colin Firth acts superbly and Mark Strong is also very good as the Doctor. As for Nicole Kidman I must confess age has done her wonders, gone is that teenage look that may have prevented here being taken seriously for "heavy" parts. The Others was a bit wooden (although the character did require that in fairness), Australia would have benefited from Nicole's more mature look. She is excellent, pulling you in to her confusion and roller coaster of emotions she goes through with each day and set of new facts she finds out. I really enjoyed this movie and would highly recommend it to anyone who likes a clever thriller without the pointless need for tons of special effects.

DON'T read spoilers, they really will ruin the film for you.