First of all, Orson Scott Card is homophobic and fucking sucks. Please donate to The Trevor Project in his name.
Now ... FULL SUMMARY WITH SPOILERS.
So it's the future, right? Like a hundred years in the future, tops. And it's all computery and people are only allowed to have two children for population control. Also, humanity was attacked by an alien bug race a few decades ago maybe, it's unclear. Humanity then retaliated, but they're all afraid the "buggers" could come attack again at any time, so the plan is to take the fight to them. Because of this, they're looking for a hero, they're holding out for a hero 'til the end of the night, and he's gotta be strong, and he's gotta be fast, and he's gotta be fresh from the fight.
So to find this hero, they're looking for a kid, because ... ??? And so they stick a "monitor" in every kid's ear so they can watch everything and determine if they're smart enough and tough enough, but also like very sweet and loving because empathy or whatever. So there's Andrew, nicknamed Ender. And he's fucking six. And they're like great, found him. Ender was a specifically requested third child in his family, because his brother Peter was too mean and his sister Valentine was too nice, but Ender is juuuuuuust right, like a little baby bear.
So Peter's a monster and tortures Valentine and Ender and he is ... an age ... I don't remember. Nine? Sure. Whatever. And Valentine is eight or whatever. And so the military is like, "Great. Ender is probably our savior, but the true test comes when we take his monitor out, but ... still ... watch him ... somehow. And so because the monitor is "out," and even though everyone thinks Ender wasn't chosen, it's fucking open season on Ender at school because now no one can be caught. Except they can. Anyway. Everyone hates this kid for being a "third." It's a nightmare. And so this fucking asshole six-year-old named Stilson come and picks a fight with Ender and Ender is like, "Welp, better shut this down right now so that I don't keep getting attacked." So he BEATS STILSON TO DEATH somehow, but doesn't realize it because after he hits him, like, twice, he runs away and reasonably assumes it's fine, but again, somehow Stilson dies? Whatever.
So at home Peter is mean. And they go to bed and then Peter comes up to Ender's bed when he thinks Ender is sleeping and whispers, "I'm so sorry, Ender. I love you I love you I love you, you're my brother." And it's very sweet, but also like, "Huh? Why?" Oh well. So the next day Commander Graff shows up and is like, "Surprise! We HAVE chosen Ender." And his parents are understandably pissed because they thought they would get to raise their son, but now they don't because he's being taken to fight school. So Ender goes and gets on a spaceship because fight school is in space. And he thinks Graff is his friend for two goddamn seconds, until Graff totally isolates him by praising Ender for being the best and smartest and booo, everyone else is so goddamn dumb. So everyone hates Ender again and Ender is understandably like, "Whyyyyyy?" And we don't know, Ender. We. Don't. Know.
So a kid is jealous and attacks him AGAIN, and Ender throws down AGAIN, and now THAT kid almost dies (does die? eh, I forget), and everyone is afraid of Ender, but also hates him. So he goes to a bunk and there are kids and whatever and one of them is named Bernard and Bernard sucks. And Bernard makes fun of this Shen kid, so Ender embarrasses him using computers, so Shen is now his friend because Shen figures out that Ender is the one who computered. Then they're sent to learn "the game," which consists of floating and shooting and squares and who gives a shit, it's even more boring than quiddich. And he makes friends with a friend of Bernard's named Alai and so now he's friends with him too. Thank fucking God.
Also he's continually playing this other different simulation by himself where he kills a giant and goes to a fairyland tower and sees himself in the mirror as Peter, and then there's a snake and the snake is Valentine, and then ... he stops or something, the game was him exercising his subconscious. It's very significant to the story, yet somehow makes no sense at the same time.
So anyway, as soon as Ender makes friends, the adults are like, "Time to make his life miserable again," so they promote him to be on a game team. (They seriously never even name the game. WTF?) They're doing this so that Ender becomes the best or whatever. So he has to try to make friends again. The captain of GAME TEAM is Bonzo Madrid and he is a MONSTER. (Why did they take Bernard, but not Peter? Unknown.) So he doesn't let Ender do anything in GAME because he sucks. But a nice girl named Petra brings him up to speed and there's a nice guy named Dink and he almost has friends again. So because Ender isn't any good at GAME yet, he forms night practices with his old friends and they all get better together. Then everyone is mad that Ender is getting better at GAME and tries to stop the practices and it's like, STFU EVERYONE YOUR BULLYING IS SO FUCKING BORING WHO CARES.
So then Ender gets promoted again because of course, but now he's a GAME CAPTAIN and oh, jeez, do they ever fuck him over this time, because they give him a bunch of rookies, one of whom is named Bean. Anyway, GAME GAME GAME, they give him too many GAME matches and it's tiring and boring. At one point, Bonzo decides to murder Ender, so Bonzo and his friends corner Ender naked in the shower room (please know that Ender is like nine). And the adults know Bonzo plans to murder him, but they're like, "You know what, let's let this play out, see how it goes." So instead Ender makes his little naked body all slippery with soap, is able to wriggle out of Bonzo's grasp and then sure enough, somehow BEATS BONZO TO DEATH WITHOUT KNOWING IT. So Ender has killed like three kids at this point. And the higher ups are like, "Great! He's our little sweetheart of a murderer!"
Oh, right, meanwhile on Earth, Peter has become kind of okay and he and Valentine are setting the stage to take over the world so that there's not a world war for control after the buggers are defeated, removing a shared enemy and need for world peace. They do this by basically becoming like Twitter and Cambridge Analytica and it's all fake propaganda and blah blah blah.
Anyway, they decide they've kicked the shit out Ender long enough, time to give him a break back on Earth. So then they bring Valentine to visit him and he's like, "Whatever, I don't want to fight their war," and Valentine's like, "Uh, hi, Ender, I'll be one of the people who die if you don't." And Ender's like, "Fuck, fine." So he goes back into space and Graff and ... someone stand over him one night and are like, "Man, we suck. We are ruining this sweet little boy. We love with this boy dearly. Oh, well. We don't want humanity to die, so let's keep pushing him to the brink of insanity." Ender is like 11 now? So then he gets this yoga military guru named Mazer Rackham, the guy who defeated the buggers in the second wave of the war. And they train train train and then they're like, "Hey, remember those friends we didn't let you keep? Now they're all on your team remotely." And Ender gets like two seconds of joy out of this, but then it's train train train again.
So they're all tired as shit, right? And then, oh boy, big day, it's Ender's FINAL EXAM. And Mazer is there and Graff is there and like every military head is there watching. And in the simulation, they come upon the bugger home planet and Ender's like, "You know what? Fuck this exam." So he plows through everyone, not caring how many men he loses, and blows up the entire planet. And Ender's thinking, "There, that'll show them." But they're all CELEBRATING. What? Turns out the whole time he's been playing the simulation, it was REAL and he just unknowingly committed GENOCIDE. JESUS FUCKING CHRIST.
So then just like Peter and Valentine thought, a war breaks out, but then Peter and Valentine end it in like, days? by using their secret propaganda identities? Great. So then it's human colonization time, Peter's President of Earth or whatever, Valentine flies to space to live with Ender, and they go back to re-populate the reformed bugger planet, which re-formed because it was a magical nuclear weapon or something. So Ender gets older and he's walking with some kid, which, who cares, this kid has no significance, whatever. And then, hey, remember that "dead giant in fairyland" game from before? Suddenly there's this expanse of the planet like looks like a crude version of that. What! So Ender goes to the tower and there's an egg and the egg communicates with him telepathically and tells him the story of the buggers. Their story is that they attacked the humans without malice, they basically thought they were taking out an ant hill. Then they were like, "Oops, this weren't no ant hill, we shouldn't have done this, so sorry, so sorry, bye." But the humans had no way of knowing that the buggers were going to leave them alone. So when Ender's forces showed up to kill them, they were like, "Oh. The humans didn't forgive us." It's legit beautiful and moving and is the only reason this book exists. So the egg queen is like, "Please tell everyone we're sorry, we hope you can forgive us, and we don't hold you responsible for our death. Please put this egg somewhere safe where we can be born again." And Ender's like, "Great, got it." So he anonymously writes a book called "Speaker for the Dead" and it's turns into a religion. And Peter's like, "Hey, loved your book, I know you wrote it, can you forgive me?" And it's nice.