Colonel Graff is shown to have a mysterious interest in a young boy named Ender. Graff orders a doctor to remove the monitor that has been implanted in the back of Ender's neck for the past three years. Ender believes that the removal of the monitor means he has failed as a candidate for the Battle School, and he feels relieved, hoping that his brother Peter will stop hating him. However, Ender has a severe reaction to the removal of the monitor and requires assistance from a nurse to calm down.
After some time, Ender returns to his class feeling dazed and experiencing the effects of the monitor's absence. The other children notice that his monitor is missing and mock him, calling him a "Third." Ender has two older siblings named Peter and Valentine, and his parents had special permission to have a third child in the hope that he would be the one they needed. Later, after school, Ender is confronted by a bully named Stilson and his friends. Ender takes control of the situation and taunts them, saying that it takes so many of them to fight one Third. Ender manages to free himself from their grip and knocks Stilson to the ground with a kick. He continues to kick Stilson while the others are frozen in shock. Afterward, Ender feels conflicted and cries at the bus stop, realizing that without the monitor, he might be no different from his violent brother Peter.
When Ender arrives home, his sister Valentine shows empathy towards him regarding the removal of his monitor. Ender and Valentine, along with the agents monitoring Ender, are concerned about how Peter will react now that the monitor is gone. As soon as Peter notices, he taunts Ender and engages him in a game called "buggers and astronauts,"
where Ender is assigned the role of the bugger, the enemy in the game. The game mimics the intergalactic war that humans are fighting against the buggers, who threaten humanity's existence. However, in the children's version, the astronauts relentlessly attack the bugger team without any chance for retreat.
Peter forces Ender to wear a bugger mask and proceeds to knock him to the ground, pressing his knee into Ender's stomach and suffocating him. Peter asserts that he will eventually kill Ender and boasts that he could also get awaywith killing Valentine. Valentine intervenes as a witness, arguing that Peter wouldn't be able to make both deaths appear accidental. Peter descends into delirious laughter, claiming that he can manipulate and deceive them easily. Later that night, while Ender is lying awake in bed, Peter returns from the bathroom and stands by Ender's bed. Ender fears that Peter will seize the opportunity to kill him, but instead, Peter whispers an apology, expressing his love for his younger brother.
The next morning, Ender doesn't feel hungry at breakfast. Colonel Hyrum Graff, wearing an International Fleet uniform, visits the Wiggins family. Graff informs them that Stilson has been hospitalized and asks Ender about the reason for his continued aggression even after Stilson fell. Ender explains that he wanted to win all the future fights to ensure that others would leave him alone. Graff offers Ender a place in Battle School, an institution located in outer space where young students are trained to become soldiers and commanders in the bugger war.
Ender's parents had already given their consent for his conception, which also meant giving permission for his enrollment in Battle School. Graff informs Ender that his parents love him but are secretly ashamed of having a third child. He explains that Ender's presence in the family home creates tension and disruption. Graff describes the nature of Battle School and emphasizes the looming threat of a major bugger attack. Although Ender initially expresses a desire to stay home, he eventually agrees to attend Battle School. Ender and Graff leave immediately, and as Ender steps into the car, his family bids him farewell.
The new Battle School students, known as Launchies, board a space shuttle. Ender already feels isolated from the other boys, who are joking around and finding things funny that he doesn't. He imagines a different reality where he is treated like a celebrity, answering questions from cameras and interviewers. Ender notices the absence of gravity and envisions himself hanging upside down from the Earth. He is relieved to see Colonel Graff join the shuttle but becomes dismayed when Graff addresses the students and singles out Ender as the smartest among them, insulting the others. The boys mock Ender's favored status, and one of them starts hitting the back of his head. Ender plans his retaliation carefully and catches the boy's wrist, causing him to flipover and break his arm. Graff uses the incident to further emphasize Ender's superiority. The shuttle docks at Battle School, and Ender waits for the other boys to leave before confronting Graff, who insists that he isn't trying to befriend Ender but will push him to be the best.
Ender enters the dormitory and finds only one bed left. He activates the voice command for the locker attached to the bed and takes stock of its contents, which include military-issued jumpsuits and non-lethal game weapons. An older boy named Dap introduces himself as their "mom" for the next few months. In the mess hall, the other boys avoid sitting with Ender, so he observes his surroundings. He notices a scoreboard that tracks the wins and losses of different teams in the games. Ender realizes that the school places more importance on these games than on academic work. The older kids wear colored uniforms according to their teams, while the Launchies have plain uniforms. That night, Ender silently cries in his bunk, grateful for the experiences he had with his brother Peter.
The next day, Ender discovers the game room and starts studying the games played by the older boys. They initially dismiss him, but Ender challenges one of them to a game and wins two out of three rounds. Bernard, the boy whose arm Ender broke, gains followers who see Ender as their enemy. Ender is disappointed by how many blindly follow Bernard. Another Launchy named Shen becomes a target of mockery,
but instead of publicly defending him, Ender takes revenge by hacking into his digital desk and sending a message warning about Bernard. Bernard knows Ender is responsible but can't prove it. Bernard loses most of his followers, and Shen becomes friends with Ender.
When Ender and the Launchies enter the battleroom, Ender starts experimenting with zero gravity. Bernard and Alai follow his lead, and gradually, the other boys join in. Ender notices Alai's strategic approach and approaches him. They become reluctant friends and are the first to discover that the laser guns in their uniforms can freeze the suits. They invite Bernard and Shen to join them, and together they freeze the rest of the Launchy group until Dap unfreezes everyone. This changes the group dynamics, with Alai bridging the gap between Bernard's followers and Ender's outsiders.
During Free Play on his computerized desk,Ender plays a game called the Giant's Drink, which is unwinnable. He explores other options but finds them boring and always ends up confronting the Giant. The Giant presents two shot glasses filled with different liquids, and Ender must choose which one is poison. Frustrated, Ender kicks both glasses and attacks the Giant, gouging out his eyes. Ender climbs into the Giant's skull, and the scene shifts, with a bat landing on the Giant's nose. The bat asks how Ender got to Fairyland, and Ender offers it a handful of the Giant's eye. Despite reaching the next level of the game, Ender signs off and hides in his bed, disturbed that he had to choose murder to avoid his own death.
Ender and Alai return to the dormitory, and Alai discovers orders promoting Ender to Salamander Army, even though Launchies are not usually promoted until they are eight years old. Ender is upset by this and Alai bids him farewell with a kiss on the cheek and a word in a foreign language, salaam, which Ender realizes is a sacred ritual from a suppressed religion. Frustrated, Ender goes to the game room and continues exploring the Fairyland game beyond the Giant's Drink.
In Salamander Army, Ender is met with surprise, but he quickly befriends Petra Arkanian, the only girl in the group. Their commander, Bonzo Madrid, is unhappy about Ender's arrival and orders him to stay out of the way during practice and games. Petra offers to teach Ender some basics after breakfast, and Ender gladly accepts. However, when Ender asks Petra to coach him during Free Play, she declines. Ender decides to practice with his Launchy friends instead, focusing on trial and error to improve their skills. Bonzo disapproves of Ender associating with the Launchies and forbids it publicly. In private, Ender challenges Bonzo's authority, giving him a chance to retract his order the next morning, but Bonzo begrudgingly complies.
During Ender's first battle with Salamander, he follows Bonzo's orders to stay in the corridor for five minutes. Once in the battleroom, Ender's legs are frozen by an opponent, but he pretends to be eliminated for the rest of the game, following Bonzo's order not to use his gun. He has an opportunity to shoot some of the remaining enemy players, which would result in a draw, but he chooses to follow orders and lets the opponent win. Bonzois confused by the fact that not all Salamander players were eliminated and realizes that Ender could have changed the game's outcome. However, Bonzo doesn't retract his orders, and Ender achieves a perfect efficiency score. Eventually, Ender grows tired of Bonzo's orders and in a game against Leopard Army, he eliminates the remaining players, resulting in a draw. Bonzo is furious and transfers Ender to Rat Army. Before leaving, Bonzo punches Ender in the stomach, causing a commotion among the other members of Salamander Army. Ender advises Petra not to be seen with him during morning practice anymore.
Graff and Major Anderson discuss their plans to manipulate the circumstances to challenge Ender and accelerate his training, even if it risks the school's credibility. Anderson expresses concerns about the school's politics, but Graff argues that if Ender doesn't develop quickly, the school's existence will be in jeopardy.
In Rat Army, Ender meets their commander, Rose de Nose, and is surprised to find their barracks in disarray despite their high game ranking. He learns that his recruitment to Rat Army was not Rose's decision but that of a toon leader named Dink Meeker. Dink trains his
toon separately from the rest of Rat Army and quietly maintains the army's reputation. Ender discovers that Dink implements Ender's strategies, even though he doesn't fully understand Ender's reasoning. Later, when Rose discovers that Bonzo oversold Ender's value during the transfer, he punishes Ender by sending him into the battleroom without reinforcements as soon as the game starts. Ender uses his limited advantage to shoot as many opponents as he can before being eliminated, drifting aimlessly for the rest of the game. Once again, Ender's performance impresses onlookers, and the rules of the game change for the entire school, with armies entering the arena instantly.
Dink reveals that he has turned down promotions because he sees the teachers as the true enemy, manipulating the students to fight and hate each other. Ender becomes more aware of this perspective, although he doesn't agree with Dink's belief that the bugger war itself is a lie. Despite Dink's request, Ender continues training with the Launchies, but they start receiving negative attention from the older boys. The older boys first engage in bathroom fights with the Launchies and later launch a full-on attack in the battleroom. The Launchies, especially Ender, successfully defend themselves, using their rehearsed coordinated attacks. Ender reflectson how he repeatedly resorts to violence to achieve his goals, both in the battleroom and in the Giant's Drink game. Some of the other commanders support Ender's practices and send their larger soldiers to protect him and train with him. That night, Ender sees his brother's face in the mirror while playing the Giant's Drink game.
Ender's progress in the fantasy game confuses Graff, as no one has reached the level beyond the Giant's Drink, and somehow the game simulates Peter's presence. Meanwhile, Valentine continues to send letters to Ender, receiving no response. She celebrates Ender's eighth birthday by burning a small fire, but the family has moved to North Carolina, making it difficult for Ender to find them. Peter directs his violent tendencies towards forest squirrels, appearing more acceptable to others, particularly their concerned mother, but Valentine sees through his facade. Peter proposes that they become a political force together, adopting online personas using their father's citizen access. Valentine initially resists but eventually agrees. They refine their writing
style and ideas on public forums before adopting aliases, Locke and Demosthenes, to write paid newsnet columns. Peter writes as Locke, the level-headed pacifist, while Valentine writes as Demosthenes, whose ideology aligns more with Peter's aggression. They ensure that their personas are interdependent. Valentine is disappointed when she hears her father quoting ideas from Demosthenes that she strongly disagrees with.
At the age of nine, Petra becomes the commander of Phoenix Army and appoints Ender as a toon leader. Older students start joining Ender's evening practices. Despite the ideal training situation, Ender is not happy. He feels a growing divide between his friends and himself, with the focus solely on intelligence and the game, lacking laughter and personal connections. Colonel Graff requests a meeting with Valentine at school, questioning her about Ender and Peter's appearance in the Giant's Drink game. Valentine feels no goodwill towards Graff but eventually reveals some vague details about Ender's relationship with Peter. She emphasizes that Ender is not like Peter, although she admits that she may be more like Peter than she wants to be. Graff asks Valentine to write a letter to Ender, reminding him that he is not like Peter.
Ender reads Valentine's letter multiple times and cries in his bed, causing confusion among his army. He then re-enters the fantasy game and conquers a level that no one knew existed- the End of the World. Graff writes to Valentine, informing her that she has been awarded the highest military honor given to any civilian. Valentine feels remorse for her involvement and believes she has betrayed her brother.
Graff and Anderson plan to rig things against Ender in the next stage of his education. Ender becomes the commander of Dragon Army, which is made up of early Launchy recruits and less notable students. Ender adopts a drill sergeant persona, resulting in the boys running naked during practice. In the battleroom, Ender redefines their understanding of gravity and establishes himself as their commanding officer. Bean, the smallest Launchy graduate, proves to be intelligent and quickly adapts to Ender's leadership. Ender starts subtly encouraging the others to resent Bean's intelligence. After practice, Bean requests his own toon,
and Ender tells him he must prove himself as a leader first. Anderson informs Ender that he can no longer hold free-for-all practice sessions, effectively isolating Ender from his friends. Ender dedicates himself to opposing the teachers, as he feels frustrated by his recurring isolation.
Dragon Army has their first battle against Rabbit Army, led by Carn Carby. Dragon Army anticipates the opponent's formations and wins the game with minimal casualties. Ender insists that morning practice begins at the same time, giving them limited time for breakfast. However, Ender allows the toon leaders to give the boys an additional 15 minutes. During lunch, the other commanders avoid Ender, but Dink Meeker approaches him and questions whether Ender's scores are a miracle or a mistake. Carn Carby tells Ender that the others are treating him unfairly and asks him to defeat the next army as a favor. Ender agrees. Dragon Army continues to win battles over the next seven days, despite facing resentment and harassment from the other armies. Graff calls Ender into his office and announces that Dragon Army will have their second battle of the day against Salamander Army, led by Bonzo. Ender improvises a strategy and easily defeats Salamander Army. Upset with Major Anderson's cheating, Ender storms out of the battleroom without paying respects to Bonzo. Ender confides in Bean about his exhaustion and assigns him an experimental task force to train. Bean stays in Ender's room for the night.
Bean experiments with twine during practice to make fast turns in the battleroom. Petra warnsEnder that Bonzo and his followers have a plot to kill him, but Ender dismisses her warning. Petra questions whether Ender knows who his friends are before leaving. Ender's veteran soldiers offer to accompany him everywhere. Ender believes the teachers will protect him from real threats, so he doesn't worry. After a morning battle, Ender goes to the showers and is confronted by a group of boys led by Bonzo. Ender appeals to Bonzo's honor and convinces him to fight one-on-one. Ender steams the room to make his body slippery and gains an advantage. He fights Bonzo and eventually knocks him out. Dink guides
Ender away from the scene, and Ender cries over Bonzo's lifeless gaze. Later that day, Ender receives battle instructions to face two armies instead of one. He disregards previous rules and traditions and focuses solely on sending his soldiers through the enemy gate. Ender wins the battle and approaches Major Anderson to accept victory. Ender cancels his army's practices permanently. Graff informs Ender that he has been promoted to Command School, and they leave for landside immediately. Ender feels that his true home is back in Battle School, unaware that Bonzo's body is being transported on the same shuttle.
The authorities, including Graff, discover that Valentine and Peter are the ones behind the Locke and Demosthenes personas, but they choose not to act on this knowledge for now. Valentine enjoys playing Demosthenes and sympathizes with his ideas. Graff meets with Valentine at school and takes her to see Ender, who has spent three months building a raft by a remote cabin. Valentine doesn't trust Graff but agrees to go. Ender and Valentine reunite, and Ender shares his frustration and exhaustion with not understanding the buggers. Valentine urges him to reconsider Command School and reminds him of the stakes. They agree to go to Command School together. They travel to the top-secret location of I.F. Command headquarters on the distant planet Eros, discussing Battle School, Command School, physics, and the buggers during the journey.
On Eros, Ender has no opportunity to make friends and spends most of his time alone or with his new teacher, Mazer Rackham. Mazer shows Ender uncensored Invasion videos and explains the theory that the buggers live in a hive controlled by the queen. Ender participates in simulations with familiar voices of his squadron leaders from Battle School,and they learn to operate as a team. Mazer tells Ender that his real education is beginning, and the simulations become more realistic. Ender experiences physical and mental exhaustion, and his health declines rapidly. During his final exam, Ender abandons the game's rules and focuses on sending his soldiers through the enemy gate. He wins the
battle, and the officers observing are moved to tears. Mazer reveals that Ender has been commanding real battle fleets and that it was the Third Invasion's final battle.
Graff is declared not guilty of crimes against the Battle School children, and he becomes the Minister of Colonization. Demosthenes advocates for Ender's return to Earth, while Locke argues against it. Valentine and Peter oppose their respective aliases' opinions, and Valentine decides to join the first colonists settling the bugger worlds, bringing Ender along. Ender agrees to govern the new colony, wanting to understand the buggers better and repay what he took from them. During the voyage, Valentine writes about the bugger war, and when they arrive, Ender works to establish a sustainable economy and learn from the buggers. Years later, Ender is asked to find a place for a new colony ship, and he discovers a hollow hill from the Battle School fantasy game. Ender finds a pupa containing a fertilized queen bugger and promises to find them a world for a second chance. Ender anonymously writes a bugger history, and it is accepted as a holy text, giving rise to a religion. Ender and Valentine continue to travel the stars, looking for a new home for the buggers.