Before I Go to Sleep, By S J Watson

Dear diary: Is that a stranger in my bed, or have I lost my memory (again!)?

Before I Go to Sleep is the first novel by S J Watson, a former NHS worker who earned a place on the Faber Academy's "Writing a Novel"' course.

He may be unknown, at least for the moment, but his debut has already attracted well-known admirers. Ridley Scott bagged the film rights and has hired Rowan Joffe to direct. Lionel Shriver, Dennis Lehane and Sophie Hannah all give excellent blurb, as does Tess Gerritsen, who gushes: "Quite simply the best debut I've ever read."

Setting aside Gerritsen's apparent reservations about Dubliners, Catch-22 and The Catcher in the Rye, these endorsements propose Before I Go to Sleep as a blend of the popular and the literary. And so it proves, although Watson's commercial instincts are keener than his prose. The high concept goes like this: every morning Christine wakes up in an unfamiliar bed beside an unfamiliar man. Spotting his wedding ring, she assumes she got drunk the night before and surrendered to adulterous temptation. Christine thinks like a twenty-something party girl, so it comes as a shock when she looks in a mirror and sees a 47-year-old woman staring back.

But she has not been on a two-decade bender. Instead, since a vaguely defined accident, she has had a faulty memory that deletes her history every 24 hours. The strange man in the bed introduces himself as Ben, her husband of 20 years. It is the first of many "revelations" Christine experiences on a daily basis: she has written a novel; given birth to a son, who was killed in Afghanistan; and she had an affair, which led to her accident. Guiding Christine through the fog is Dr Edmund Nash, a neuropsychologist. Having introduced himself each morning, he tells Christine to read her journal. Its first words are: "Don't trust Ben".

Readers have seen this sort of thing before. Offbeat mental states doubling as ingenious narrative devices are all the rage in contemporary cinema: Memento, Groundhog Day, Eternal Sunshine of the Spotless Mind, and the Japanese film Yogen (remade as Premonition). The popularity of the conceit is appropriate given that most of the above are concerned with repetition. These vivid merry-go-rounds only stop spinning when some original sin is uncovered.

Watson's take on the material is clever, convincing and moreish. Christine's life is mundane, but filled with tantalising possibilities: the early chapters fly by as you wonder exactly who to trust. The fun comes from spotting the plot holes that Watson later exploits for all they're worth. Why is Ben untrustworthy? Is Dr Nash's interest purely professional? And where are the social services, or Christine's friends and relations?

Christine's journal is a smart way to dish out clues, and to provide another layer of uncertainty that cracks like an egg: can she even believe the evidence of her own pen? But as the plot quickens, the need to have Christine reading her way to enlightenment slackens the tension. In the final, violent climax, a character has to dash out for champagne and then conveniently jump into a shower, simply to allow Christine the time to excavate vital information.

The ending feels hurried; a sentimental postscript to the meticulously plotted main event. But these are minor gripes. Before I Go to Sleep is an enjoyable and impressive first novel. Like the best of its thematic predecessors, it is also an affecting moral allegory: don't forget your loved ones. Or else.