In the future, humanity is preparing to launch an attack on the homeworld of an alien race called the Formics who had attacked Earth and killed millions. Over the course of fifty years, gifted children are trained by the International Fleet to become commanders of a new fleet for this counter-attack.
Cadet Andrew "Ender" Wiggin draws the attention of Colonel Hyrum Graff (Harrison Ford) and Major Gwen Anderson (Viola Davis) by his aptitude in simulated space combat. They order the removal of his monitor, signifying the end of the cadet program. Ender is attacked by Stilson, a student he defeated in the combat sim, but Ender fights back and severely injures him. Ender confesses his grief to his older sister Valentine, but is harassed further by their older brother Peter. Graff arrives to reveal he was being tested and is still part of the program. Graff brings Ender to Battle School, placing Ender with other cadets his age, but treats him as extraordinary, ostracizing him from the others.
Among other studies, the cadets are placed in squads and perform training games in a zero gravity "Battle Room". Ender quickly adapts to the games, devising new strategies older students have not yet seen. Graff reassigns Ender to Salamander Army, led by Commander Bonzo Madrid. Bonzo is resentful of the new addition and prevents Ender from training. Another cadet, Petra Arkanian, takes Ender and trains him privately. In one match, Ender goes against Bonzo's orders and works with Petra to achieve a key victory for his army.
Meanwhile, Ender plays a computerized "mind game" set in a fantasy world aimed to present difficult choices to the player. In one situation, Ender creates an outside the box solution to overcome a seemingly unsolvable problem. Later, he encounters a Formic in the game, and then a simulated image of Valentine entering the ruins of a castle. Inside, he finds another image of Valentine but as he nears, it turns into an image of Peter before the game ends.
Graff promotes Ender to his own squad, made from other students that have gained Ender's trust. They are put in increasingly difficult battles. In one match against two other teams including Bonzo's squad, Ender devises a novel strategy of sacrificing part of his team to achieve a goal, impressing Graff. Bonzo accosts Ender in the bathroom after the match, but Ender fights back and Bonzo falls during the struggle, accidentally paralyzing him. Distraught over this, Ender prepares to quit Battle School, but Graff has Valentine speak to him and convince him to continue.
Graff takes Ender to humanity's forward base on a former Formic planet near their homeworld. There, Ender meets Mazer Rackham, who explains how he spotted the shared-mind nature of the Formics to stop the attack fifty years prior. Ender finds that his former squad members are also here to help him train in computerized simulations of large fleet combat; Rackham puts special emphasis on the fleet's Molecular Detachment (MD) Device that is capable of disintegrating matter.[note 1] Ender's training is rigorous and Anderson expresses concern they are pushing Ender too fast, but Graff notes they have run out of time to replace Ender.
Ender's final test is monitored by several of the fleet commanders. As the simulation starts, Ender finds his fleet over the Formic homeworld and vastly outnumbered. He orders most of his fleet to sacrifice themselves to protect the MD long enough to fire on the homeworld. The simulation ends, and Ender believes the test is over, but the commanders restart the video screens, showing that the destruction of the Formic homeworld was real and Ender had been controlling the real fleet this time. Despite Graff's assurance he will be known as a hero, Ender is furious as he feels responsible for the annihilation and everyone will remember him as a killer.
As Ender struggles with his emotions, he recognizes one of the Formic structures nearby similar to the ruined castle from the game, and believing they were trying to communicate with him, races out towards it. He follows the path set by the game, and encounters a dying Formic queen who has been protecting another queen egg. The Queen acknowledges that while Ender carried out the genocide of her race, he had only wanted peace in the long-term and forgives him.
Ender writes in a letter to Valentine that he is heading to deep space with the egg, determined to colonize a new Formic world with it.
- Asa Butterfield as Andrew "Ender" Wiggin
- Harrison Ford as Colonel Hyrum Graff
- Ben Kingsley as Mazer Rackham
- Kyle Russell Clements as Young Mazer Rackham
- Hailee Steinfeld as Petra Arkanian
- Abigail Breslin as Valentine Wiggin
- Viola Davis as Major Gwen Anderson
- Aramis Knight as Bean
- Suraj Parthasarathy as Alai
- Moisés Arias as Bonzo
- Khylin Rhambo as Dink
- Conor Carroll as Bernard
- Nonso Anozie as Sergeant Dap
- Jimmy Pinchak as Peter Wiggin
- Nonso Anozie as Sergeant Dap
- Andrea Powell as Theresa Wiggin
- Caleb J. Thaggard as Stilson
- Jasmine Kaur as Professor
- Tony Mirrcandani as Admiral Chamrajnagar
- Brandon Soo Hoo as Fly Molo
- Cameron Gaskins as Pol Slattery
- Orson Scott Card as Pilot
- Gavin Hood as Giant