Ender, the third child in a society where only two children are allowed per family, has been monitored for aptitude because the government needs children to go to a special training academy and learn how to fight aliens, which have been at war with Earth. His older brother hates him for performing better in the examination. Ender's monitoring device is taken out and he brutally beats a bully at school, which ends up killing him later on, without Ender's knowledge. Ender is notified the next day that he has passed the exam and will be taken to the training facility. On the shuttle ride into space, Ender breaks someone's arm on accident when they make fun of him for being a genius. In space school, Ender is bullied again. The students begin to test out the battle room, which is a zero-gravity space for practicing combat maneuvers. As soon as Ender begins to make friends, he is transferred to a different squad. He makes friends with Petra, the only girl in the squad. Ender learns how to shoot and play the battle game, but his new squad is not as effective as the last one. Ender is traded to another team. He runs practice sessions with other young boys so they can become stronger soldiers. A few years later, at the age of nine, Ender is leading the Phoenix Army training squad. One of the adults at the facility gives Ender an army, Dragon Army, that has been discontinued for a while. He is a year and a half younger than most other commanders. Even as he wins many battles, others resent him for his success and he finds it hard to make friends. He watches videos of past alien battles to learn how the other side fights. Ender mentors a younger boy named Bean. Ender's brother and sister form a truce and conspire to influence the political order together by posting political diatribes using pseudonyms. They soon become monstrously popular, but no one knows that they are children. A group of boys tries to kill Ender in the bathroom, but he beats them. Teachers begin manipulating the games and making them unfair to upset Ender. He receives a notice saying that he is graduating early. Most students don't go to command school until they are sixteen. A conversation between commanders reveals that they know Ender killed his school bully, but they decided not to tell Ender this to preserve his mental state. Ender is allowed to visit his sister back on Earth. He transfers to command school on another planet and plays another computer simulation, but finds it to be too easy. He is introduced to a war hero who teaches him how the aliens operate, communicate, and fight. Ender begins to command a squadron of his friends from the battle school. One day, Ender is told that he is to be examined by officials as he plays a war simulation. He takes many risks during the game and explodes the simulation of a planet. When he gets out of the simulation, he is shocked to find the officials celebrating, as he believes that he cheated the rules in order to win. His mentor tells him that the games were not games. Ender was the commander of the military's fleet this entire time, and simulations he played were actual alien battles. The planet he just exploded in the game was the actual home planet of the aliens. The war is over and Ender won it for the sake of humanity —without even knowing it. Ender is horrified because he killed unknown numbers of aliens, including civilians and children. War nearly breaks out on Earth because of tension between countries, but it is narrowly avoided. It is hinted that the countries accepted a proposal set out by Ender's siblings using their fake names. The leaders of the schools discuss what is next for them. The public was angry for a while about their mistreatment of children. The men plan to colonize the alien's planet, as the soil is fertile and all the aliens are dead. Ender's sister comes to visit and explains that she has retired her pen name and is no longer involved in politics. She tells him that Ender's abusive brother now controls much of the global political sphere because he is a genius. He wants to use Ender, but she blackmailed him into letting her and Ender fly to another planet and live in the aliens' abandoned colonies. Ender is set to be the governor of the new colony. His new goal is to understand how the aliens lived so he can properly grieve all that he stole from them. Eight years later, Ender is on the aliens' planet and discovers a strange playground and natural formation. He recognizes it from a video game he played in the first battle school, when he was six. He believes that the aliens built it for him as a sort of revenge before their death, though it is unclear how this could be possible. They must have been able to read his dreams, as he dreamed of the game often. He walks into a structure and has a disturbing vision of helping the larva of a new queen alien survive so that she can birth thousands of more aliens. He finds a cocoon with a new queen but doesn't want to help her. She explains telepathically that they did not know they were killing humans in the first invasions; they did not know that humans are sentient. She forgives him for what he did, so Ender takes the cocoon and promises to take it to another planet. He becomes an advocate for this nearly-extinct species as a means of repairing the damage done between the two species that arose from a simple inability to communicate.