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“Before I Go To Sleep” is a risky title for a genre exercise intended to keep viewers bolt upright in their seats, handing mirthful critics a ready-made punch line at the first sign of lethargy. The good news is that Rowan Joffe’s adaptation of S.J. Watson’s 2011 publishing phenom is far from a snooze; the bad news is that it’s the film’s escalating ludicrousness that holds our attention.

Starring Nicole Kidman as a short-term-memory amnesiac unsure whether she’s being played by her husband, her shrink or both, the film’s premise could be more pithily described as “Alfred Hitchcock Presents: 50 First Dates.”

For the bulk of its running time, “Before I Go to Sleep” is a psychological puzzle picture, reserving the would-be white-knuckle stuff for its final few reels. The narrative’s complex network of holes is so apparent by that point that any real sense of peril is hard to sustain despite the quivery efforts of Kidman. Having already impersonated Grace Kelly in one bad film this year, she has a second bite at the apple here: Her vulnerable, terminally addled but resourceful heroine Christine Lucas is essentially a terrorized Hitchcock blonde in sensible shoes.

There’s a Cary Grant substitute, too, in Colin Firth’s stiffly affectionate, not entirely forthcoming husband figure Ben, whose dulcet tones provide much of the initial exposition. Christine , it turns out, has suffered from anterograde amnesia ever since nearly losing her life in a horrific attack several years prior. Every day she wakes to become freshly acquainted with Ben and the moneyed, minimalist house they share in outer suburban London; whatever new information she gleans during the day is wiped clean by morning.

What Ben doesn’t know, however, is that Christine has been keeping a video diary at the behest of her psychologist, Dr. Nash (Mark Strong), a device that allows her some semblance of cumulative memory. “Sleep” opens with her recording a particularly panicked bedtime entry before skipping back to the recent past. Nash calls Christine on a daily basis to reintroduce himself and remind her of the diary’s existence. In this way, she pieces together fragments of her personal history that Ben, supposedly out of concern for her mental well-being, has kept from her — notably her estranged best friend, Claire (Anne-Marie Duff), and, crucially, her departed son Adam, whom Ben claims was lost to leukemia some time after her accident.

Christine inches toward the root of her trauma; furthermore, at a sort of one-step-forward-two-steps-back pace, she begins to realize that her domestic life is not what it appears to be. To unpick the numerous lapses in logic and credibility that keep this plot suspended — most of them, to be fair, inherited from the source novel, from which Joffe’s screenplay makes few drastic deviations — would be to enter severe spoiler territory. It is fair, however, to note that the film never answers the question of how Nash, without the knowledge or consent of the keenly protective Ben, came to treat Christine in the first place.

Performance-wise, the film is constructed as “The Kidman Show,” though the star’s deliberate turn isn’t always in sync with the more histrionic demands of the filmmaking or the film’s jumpy score. Strong offers a warmly neutral bedside manner, while Firth seems detached beyond the requirements of his role. With “Sleep” coming not long after his and Kidman’s more attentive collaboration in “The Railway Man,” in which Firth’s character was the one with psychological demons to exorcise, these well-matched co-stars have surely earned the right to have a little more fun together — or, failing that, at least a good restorative nap.

“Before I Go To Sleep” – 2 stars

MPAA rating: R (for some brutal violence and language)

Running time: 1:32

Opens: Friday