It's 2070, forty years since a devastating alien invasion was barely turned back, and the world is desperately searching for soldiers to lead them to victory when the "Buggers" come again. That's why they're drafting young children who pass a rigorous screening, and sending the best of them to the orbiting Battle School, where they are trained from childhood to be ready for war in the vertiginous reaches of space.
Into the unending pressure of military training comes six-year-old Andrew "Ender" Wiggin, who struggles to keep his humanity even as the adult teachers, rivals among his fellow students, and the strange unseen influence of the alien invaders all threaten either to destroy him or to make him into someone he can't bear to be.
His genius raises him to the top of the intensely competitive games in the Battle Room, an immense null-gravity chamber where armies of youngsters engage in mock combat. But his real struggles are off the playing field - with a dangerous older boy named Bonzo Madrid who is determined that both he and Ender cannot survive in this place; with his teacher, Mazer Rackham, who won the last war on a fluke and now is trying to prepare Ender to win the next one by skill rather than luck; and with himself, as Ender wrestles with his own demons, desperate to remain a decent human being even as he sees himself being transformed into exactly the same kind of monster as the buggers themselves.