In the near future, Earth has narrowly survived an attack from a technologically superior alien race known as the Formics. In preparation for a feared second invasion, the world's military forces have banded together to form the International Fleet, a global organization tasked with finding and training future fleet commanders. The most promising children are identified and recruited from a young age, sent to Battle School in orbit around Earth to undergo a rigorous military training program. One such recruit is Ender Wiggin, a shy but strategically brilliant boy whose unique talents place him under the tutelage of Colonel Hyrum Graff, the commander of the training facility, and Major Gwen Anderson, a psychologist who monitors the children's emotional well-being.

Within the Battle School, Ender struggles to fit in among other gifted trainees and faces intense pressure to succeed. His ingenuity and tactical genius quickly earn him respect and lead to rapid advancement through the ranks, though they also cause friction with his peers. Throughout his training, Ender is put through a series of increasingly complex war games in the Battle Room, a zero-gravity environment where students learn the fundamentals of space combat. These simulations are designed to test the recruits' abilities to think strategically and work as a unified force, all in preparation for the looming threat of another invasion by the alien enemy.