The people of a small town suddenly find themselves trapped in a bubble. How they react to this dilemma is the main part of the story while trying to figure out why is it happening is a secondary concern. This was one of Stephen King's most massive books. He also felt the story needs to be stretched out on TV and should span several seasons.
For those fans of The Simpsons Movie you may remember a similar plot but everyone involved agrees it was just a coincident. Another trapped in a fish bowl movie that I enjoyed was Dark City and may be a bit of spoiler to the book.
The book is guaranteed to be different than the series as King himself said that the book ending and reasoning would not work well on TV. Still I would wait to read the book if you have not yet. I find it better to read the book later as people tend to be disappointed with the TV/Movie versions.