This is a 5 of the page-turner variety. It's a little bit of a horror novel, but it's Card so it's still a little sweet (if you've read the sequels to Ender's Game, you know what I'm talking about). If you're a computer person, you may giggle a little, as the main character is a programmer and this was written in 1980-something.
A brief synopsis: Step Fletcher, his wife DeAnne, and their 3.5 children (DeAnne's preggers) move to North Carolina so Step can start a new job. Turns out, a bunch of little boys around their oldest son's age have been disappearing. Also, Stevie is tormented by his teacher and fellow students so he only plays with his imaginary friends. But soon you have to ask the question, "How imaginary are these friends?" dun, dun, dun!
You should definitely read it. Fair warning: you'll need a Kleenex at the end.
What is the saddest book you've ever read?