I have read all four of the books in this series and loved them. Could not get through one and to the next soon enough (which was quite a task as these books are huge).
It is a story about a virtual world where children are being trapped. The sister of one of these children goes into this alternate world to find out what has happened to her brother before it is too late. During her search she meets a band of people who for various reasons of their own want to find out and stop whatever it is that is causing children to go into comas. It is a non-stop journey with an amazing ending that you will never forget.