Fiction by Orson Scott Card.
This is a "direct sequel" to the book Ender's Game, the early-eighties science-fiction novel recently made into a film.
First of all, Ender's Game itself is a great book. And the movie didn't stink.
Also I liked this book as well. But you have to have the background of the other book to enjoy it. At least Ender's Game, if not more of them.
The thing is, this author has already written a full trilogy of not-so-direct sequels, along with a series of (5) parallel novels, set in the Ender universe. (All of which I have read by the way, and loved. ) But some people might find a set of ten books a bit excessive. (Not I, said the cat.)
NOTE: (For a handy chart on the order of the Ender novels, see my later review of Shadows in Flight.)