Earth
Each chapter of Ender's Game opens with a conversation between the government officials who are responsible for finding a military genius to lead Earth to victory against the alien "bugger" fleet. From these conversations, the reader learns that Andrew "Ender" Wiggin is considered humanity's best hope for such a leader. It is also made clear that these officials will isolate and test Ender as much as possible to mold him into the effective military leader they so desperately need.

Ender's story opens as he is finally losing the monitor implanted in the base of his neck, a device which allows government officials to see and hear whatever he experiences. He is later than most in having the device removed—six years old—thus separating him from his peers. He is also the third child of his family, in a futuristic society that seldom allows more than two children. Although Ender is a legal "Third," he is still an object of scorn and derision. After the monitor is removed, an older, bigger boy, Stilson, leads a group of bullies against Ender. Ender fights him viciously, attempting to discourage further attacks in the future. (The fact that Stilson dies in the process is not revealed until the book's later chapters.)

At home, Ender's older sister Valentine sympathizes with him, but his sadistic brother Peter brutalizes him and says that someday he will kill Ender and Valentine. The following day, Colonial Hyrum Graff of the International Fleet comes to the house and convinces Ender to accompany him to Battle School. There he will train to fight the Buggers, a race of insectlike aliens that has invaded Earth twice already and nearly destroyed humankind. Ender agrees to go, due to a combination of three things: love for his sister; fear of his brother; and the knowledge that his conception as a Third was only allowed because it might produce a qualified candidate for the school. In the spaceship that takes new cadets to the orbiting Battle School, Graff shows preferential treatment to Ender. An older boy bullies Ender because of this, and Ender responds too hard for the weightlessness of space, breaking the other boy's arm. Even before entenng the school, Ender has once again been set apart from the other children.

Battle School
From the first, Ender is the object of bullying at Battle School, in part because the school's leaders intend for him to be isolated and feared. He wins some respect by devising clever new strategies in battle simulation games and for cracking the security codes on his tormentors' computer files. He and his fellow beginners, called "Launchies," are finally introduced to the null-gravity battleroom, where the older recruits learn strategy by conducting battles against each other's armies. Just as Ender begins making friends, he is promoted from the Launchies into a student army, the Salamanders. Not quite seven, he is at least a year early for the promotion. He becomes an outcast once again; his commander, Bonzo Madrid, forbids him to participate in battles and vows to trade him away at the earliest opportunity.

A fellow soldier in his army, Petra Arkanian, helps Ender learn some of the basics of fighting in the battleroom. Forbidden to work with the Salamander Army, Ender begins practicing with his old Launchy comrades. Ender later wins a crucial battle by disregarding Bonzo's orders. From then on, Ender's imaginative strategies draw attention to him as he is transferred from one army to another, absorbing effective and ineffective military techniques by observing his commanders. Some of the older children resent him, however, and try to break up his Launchy session. He is once again forced into violence to protect himself. The frustration he feels spills over into the fantasy computer game he plays, and Ender fears he is becoming a cold-blooded killer like his brother Peter.

When Ender is given command of his own army it is not, as usual, manned with soldiers from other armies, but is filled with new recruits; they are inexperienced but intelligent and inventive, and not held down by outdated strategies. The maneuvers Ender devises are imaginative...