I picked this up after reading Dolce Bellezza's amazing review and I'm glad I did.
The plot is fairly simple: A woman, Christine, lost the ability to remember her past and form new memories following an accident in her late 20's. Her loving husband, Ben, takes care of her and patiently explains her life day after day, going so far as to place photographs of her life around her bathroom mirror and make a scrapbook for her to review. She is also seeing Dr. Nash, a young doctor who sought her out for treatment of her memory loss because he wants to write a paper on her condition.
Or so she's told. The genius of the story lies in the fact that, along with Christine, the reader realizes very quickly that nothing, not even the most basic pieces of information, can be taken at face value. With the exception of feelings and flashes of memory that may or may not be reliable, everything Christine learns about herself is at least secondhand, if not even further removed.
First, Christine's primary source of information is her journal. Since her memory lasts about a day and ends when she falls asleep (though not during a light sleep, apparently), her only way of "remembering" the things she learns is to write them in her journal. But believing the information in the journal involves believing that she actually wrote it, that the information she recorded was the truth (at least as she saw it), and believing that the journal hadn't been tampered with. The veracity of the entries is drawn into question even more when Christine learns that in the early days after the accident, she suffered from paranoia and confabulation (or, more simply, false memories). In other words, it becomes clear early on that even the most basic assumptions may very well be false because a key fact might be false. An unaffected person might easily deduce "if X, then Y," but Christine might either be unable to remember what X is or else she mistakenly thinks A is X, leading her to believe "if X, then B." (I really need to review logic better...)
Second, all information she receives is at least secondhand, if not even more removed. This means that in the most benign situations, she might receive incorrect information simply because someone else remembered it incorrectly. She might also receive incorrect information because someone was lying to protect her or, as in a couple of cases with Dr. Nash, because information he either found in Christine's file or discovered from Christine herself turned out to be false. Or, in other cases, someone who should be a reliable source appears to confirm something when in reality, he or she has made an incorrect assumption about what Christine knows, is asking, or was told.
All in all, it makes for a narrative where everyone, even Christine herself, is suspect. Since the majority of the story is told through her journal, it creates a unique situation where the reader is learning about and reacting to Christine's life at the same time that Christine is and that the reader feels the same frustration and confusion that Christine experiences when she is unable to recall or understand key facts. It also makes the journal the center of both the novel and Christine's life. Christine, to the readers knowledge, went two decades without connecting two days together or every learning enough about her life and current situation to question it. (Of course, it's entirely possible that Christine discovered the truth multiple times and forgot it.) The journal is the key to all of this and if something happens to the journal, everything is reset. Christine forgets all the information she has managed to piece together and she goes back to a blank slate (with the exception of a few childhood memories).
There's a strong feeling of racing against time and something (or someone) unidentified. The only way that Christine can retain her knowledge is by recording it in her journal. She's forced to find a way to write everything down before she falls asleep again, because everything is lost if she doesn't. Since she decides early on to hide the journal from her husband, this means that she has to find a way to hide both the act of writing and the journal itself from her husband.
I absolutely adored this book and finished it in about a day. Moreover, I found myself eagerly engaged in the story, worrying that the journal would be discovered before the entire truth was revealed and actively trying to figure out what, if anything, other characters were hiding. At around page 123, it suddenly clicked that no one would be trusted, not even Christine. (There's wasn't a particular memorable event at that point that triggered the feeling, just a eureka type moment where everything I had learned up to that point just gelled.) After reading about three-quarters of the book, I suddenly stopped and realized that the biggest concern wasn't the fact that Christine might be killed by the person (or people) manipulating her. My biggest fear was that the journal might be destroyed and Christine would permanently revert to where she was when the story began. That fate would somehow even less satisfying than Christine's death.
Reading Before I Go To Sleep was definitely not a passive experience. The story wasn't frightening, though the issues it raised about memory were definitely disquieting at some point. Overall, it was a fascinating experience and if this is any indication of S.J. Watson's abilities, I hope she publishes many, many more books.