Eleven years ago, wizards rejoiced all over the world, and Muggles (non-magic folk) were confused. They celebrated because He-Who-Must-Not-Be-Named was defeated. In other words, Voldemort (the evilest wizard around) killed Harry Potter's parents, but for some strange reason, he couldn't kill little baby Harry. Now Voldemort seems to have disappeared. Overnight, baby Harry has become a hero – "The Boy Who Lived." Having lost his family and home, Harry also has become an orphan. Dumbledore (the principle of Hogwarts School of Wizardry and Witchcraft), Professor McGonagall (a teacher at Hogwarts), and Hagrid (a groundskeeper at Hogwarts) find a home for baby Harry with his Muggle extended family, the Dursleys.
Cut to present day, when ten-year-old Harry lives with his super-mean aunt and uncle and their son Dudley. When they go to the zoo for Dudley's birthday, Harry encounters a sympathetic snake. He's able to speak to the friendly reptile and somehow seems to have removed the glass from its cage, so it can go back to Brazil. After the trip to the zoo, mysterious letters start arriving for Harry. His uncle, Mr. Dursley, is furious and tries to keep them from Harry. But the letters keep arriving at such a rapid rate that, the evening before Harry's eleventh birthday, his uncle takes the whole family to a deserted island to escape all of the mail.
They can't hide for long, though; Hagrid shows up on Harry's birthday to deliver the letter, and the news that Harry's a wizard and has been admitted to the Hogwarts School of Witchcraft and Wizardry. The next day he takes Harry to shop for school supplies at Diagon Alley, where Harry learns more about the wizarding world. He meets Malfoy (a bully) and Hogwarts' new Defense Against the Dark Arts professor, Quirrell. Harry also buys his first wand. Sweeeet. Hagrid also picks up a mysterious package at Gringotts, the goblin bank.
Later that summer, Harry travels to Hogwarts. He has to take a train from platform nine and three-quarters, a magical platform! A family called the Weasleys helps him find his way, and he begins to make friends with one of their sons, Ron. He meets other first-year students like Hermione Granger and Neville Longbottom.
Upon their arrival at Hogwarts, the first years are Sorted into one of four houses (think dormitories). Harry, Ron, Hermione, and Neville are all Gryffindors (a house known for bravery); Malfoy is a Slytherin (a house known for ambition, and infamous for producing dark wizards). They begin taking all kinds of classes in magic. Harry dislikes the Potions teacher, Snape, who is unfair and kind of mean.
Harry learns that there was an attempted robbery at Gringotts bank, but nothing was taken. He guesses that the robbers were after what Hagrid picked up. Hagrid lets it slip that it has something to do with someone called Nicolas Flamel.
Malfoy becomes a big bully. During their first broom-flying lesson, he teases Neville. In defending Neville, Harry realizes he's a natural at flying. He's a superstar on a broomstick. Although Harry's broken rules by flying unsupervised, Professor McGonagall rewards him by putting him on the Gryffindor Quidditch team as Seeker (a very important position on the team).
Later, Malfoy and Harry have a fight, and Malfoy challenges Harry to a wizard duel at midnight. Hermione and Ron accompany Harry, but Malfoy doesn't show – he was trying to get them in trouble for roaming the school while they should be in bed. As they hurry to get back to the dorm, the three friends stumble into a forbidden part of Hogwarts, where they bump into a three-headed monster dog. Luckily, they escape in the nick of time.
Harry and Ron aren't getting along with Hermione, but make up when they rescue her from a troll that's terrorizing the school. Though they get in trouble to taking on the troll alone, they also show their bravery. Now the three are inseparable.
As the first Quidditch match approaches, the three friends suspect Snape of wanting the package from Gringotts. During the game, Harry's broom acts weird and seems to be hexed. Harry's saved, but his friends blame Snape for putting him in danger.
During the winter break, Harry stays at Hogwarts and is given an invisibility cloak that once belonged to his dad. He uses it to sneak around the castle and discovers the Mirror of Erised in one of Hogwarts' many secret rooms. When he looks into the mirror he sees his parents, but when he shares the mirror with Ron, Ron sees himself as a hero. Dumbledore catches Harry at the mirror and explains that the mirror shows you your heart's desire. The wise old wizard then says he's going to take the mirror away because it's dangerous.
When classes resume after winter break, Harry, Ron, and Hermione figure out who Flamel is – an alchemist and the only person in the world to have the Sorcerer's Stone, which can provide immortality. They decide the Stone must be what was hidden at Gringotts and is now being guarded by the three-headed dog.
When not trying to solve the mystery of Nicholas Flamel, Harry is trying to balance Quidditch and school work. Gryffindor wins another Quidditch game, which Snape referees, and then Harry hears Snape and Quirrell arguing.
Meanwhile, Hagrid adopts a dragon, which is illegal. Ron, Hermione, and Harry have to convince him that's it's just not practical to raise a baby dragon, and find a way to smuggle the dragon out. Malfoy spies on them and tries to turn them in. When Harry and Hermione have successfully sent the dragon out in the middle of the night, they're caught by McGonagall – along with Neville, who was trying to warn them, and Malfoy, who tattled – and are given really big detention. Gryffindor moves to the last place in the house cup contest, and everyone is really mad at them.
Harry, Hermione, Neville, and Malfoy have detention with Hagrid in the forest at night. They are supposed to figure out what's killing unicorns and drinking their blood. Harry runs into some centaurs who see trouble ahead in the stars. They all realize that Voldemort is trying to return and that he's the one killing unicorns.
After the first-year exams, Harry, Ron, and Hermione talk with Hagrid and realize that he said too much about the Sorcerer's Stone to the mysterious stranger who gave him the dragon. Harry, Ron, and Hermione suspect that Snape is after it. That night they try to retrieve the Stone. Neville attempts to stop them, so they have to temporarily paralyze him with magic. They pass by the three-headed dog by playing it music, only to meet with another series of challenges. First, they're trapped by a Devil's Snare plant, then they have to catch a flying key, and then they have to play a life-size game of wizard chess. The chess game takes Ron out, leaving Harry and Hermione to solve a logic puzzle and drink potions to go forward. There's only enough for one, so Harry moves on and sends Hermione back for help.
To Harry's surprise, he runs into Quirrell, not Snape like he thought he would. Quirrell reveals that Voldemort is living in him like a parasite. (Eek!) He tries to use Harry to get the Stone. He makes Harry use the Mirror of Erised, and Harry finds himself holding the Stone and lying about it. Quirrell/Voldemort tries to kill Harry, but when he touches Harry, he burns. Harry blacks out.
When Harry comes to, he's in the infirmary with Dumbledore, and Quirrell is dead. Dumbledore explains that Harry defeated Quirrell/Voldemort through the protection of his mother's love. He also mentions that the Stone has been destroyed.
Later, at the end-of-year banquet, Dumbledore praises Ron, Hermione, Harry, and Neville for the parts they played in defeating Quirrell. He rewards them by giving Gryffindor house tons of points. They win the house cup for Gryffindor, and even pass all of their exams. Then, they leave Hogwarts for the summer and part ways at the train station. Though it stinks to be returning to the Dursleys, Harry explains how much easier his time with them will be now that he can do magic.