Humanity is close to being wiped out.
Earth has been attacked several times by an unrelenting race of aliens. The governments on earth know that the next time those aliens attack, all humankind will perish. There are military schools where very young boys are recruited and trained to become expert spaceship fighters. The government drafts a very young boy named Andrew Ender Wiggin and places on him the huge burden of saving the human race. In Ender s training, he participates in futuristic types of practice combat and military games.