Schrodinger's Baby, by H.R. McGregor (1999)
I won't spend a lot of time trying to explain about Schrodinger's cat; it's a puzzle I only partially understand and I don't want to risk the mocking tones of those of you who spent time in the science department while I was mooning around the library reading D.H. Lawrence. Besides, this book does a pretty good job of explaining it, I think. The gist of it (and jump in any time to correct me, science experts) is that whenever there's more than one possible outcome to something, it's difficult to say at what point the final outcome separates itself from the possibilities and becomes reality. Go a step further and maybe you'll hit upon the theory that all possible outcomes do in fact occur, splitting the universe each time into as many universes as there are possible outcomes.
In this book, this theory is applied to nearly everything that happens. There are mysteries and lies all over the place, and they all begin when the narrator, Juliet, finds a corpse in the closet. By the time she collects herself and realizes she should call the police, the corpse has vanished. As you can imagine, it's tough after something like that to know whose shifty eyes mean what. Since the people with shifty eyes are her girlfriend and her best guy friend, she doesn't know whether to drop it or pursue it. Of course she pursues it, and eventually she learns the truth. I thought it was a great mystery and a great read, and it made me want to start over again at the beginning so that this time through I could identify the clues.
The Pilot's Wife, by Anita Shreve (1998)
I appreciated the way this book got right to the point: by the third page of text, Kathryn Lyons knows that her pilot husband's plane has exploded. After that, it's one painful discovery after another, until Kathryn realizes the man she was married to might as well have been a total stranger. This is not the book for you if you've been having doubts about what a partner might be up to these days.