Warning: Official policy states that no spoiler tags should exist on recap pages. Read at your own risk.
In 1981, the Dark Lord Voldemort kills James and Lily Potter, and tries to kill their infant son Harry, but somehow fails and disappears, at which the Wizarding world celebrates. Albus Dumbledore, headmaster of Hogwarts School of Witchcraft and Wizardry, leaves Harry on the doorstep of his non-magical aunt and uncle, Vernon and Petunia Dursley, with a letter explaining the situation. However, the Dursleys dislike the idea of magic and would prefer to forget that it exists. They take out this resentment on Harry, belittling him and neglecting him at every turn, and lie to him about his parents' deaths, claiming that it was a car crash.
As Harry approaches eleven, he begins receiving invitations to attend Hogwarts, although the Dursleys intercept and destroy them. Eventually, Rubeus Hagrid arrives in person, delivers the letter, and explains to a shocked but delighted Harry that he's a wizard, before taking him to buy school supplies, from cauldrons to robes to spellbooks. Harry receives a postal owl as a gift, whom he names Hedwig, and is chosen by a magic wand that turns out to be a "brother" to Voldemort's wand (i.e. containing a feather from the same phoenix).
The Hogwarts Express train is accessed via a magically hidden Platform 9 3/4 at King's Cross Station; Harry is unaware of how to find it but encounters the friendly and numerous Weasley family, who help him through the barrier and onto the train. Ron Weasley, who is Harry's age, shares a compartment with him and begins explaining various aspects of magical life. Draco Malfoy, also their age, turns up and offers to help Harry meet "the right sort", but Harry, displeased by Draco's dismissive attitude toward the Weasleys and toward non-magical people, rejects the offer. Hermione Granger also drops by, looking for another student's lost toad, and shows herself to be well-meaning and studious, but bossy.
Harry, Ron, and Hermione are sorted into Gryffindor House, home of the chivalrous and brave, although the Sorting Hat informs Harry that he would do well in Slytherin, house of the cunning and ambitious, which would "help you on the way to greatness"; Harry rejects the idea because Ron has warned him that Slytherin is known for producing dark wizards and witches. Draco is sorted into Slytherin, without any hesitation. While at the Sorting feast, Headmaster Dumbledore warns the students not to enter the Forbidden Forest or the third-floor corridor on the right-hand side.
Classes begin, with Harry's performance being generally reasonable. He finds that the Potions master, Professor Snape, has an immediate antipathy toward him, but he excels in flying broomsticks, accidentally winning a spot on the Gryffindor Quidditch team despite being a first-year. Draco, meanwhile, shows a tendency toward bullying, particularly harassing Neville Longbottom, who was sorted into Gryffindor but is shy and self-deprecating. Hermione is very intelligent but alienates most of her classmates with her brusqueness and know-it-all attitude.
After they exchange harsh words, Draco challenges Harry to a duel after curfew, which Hermione is unable to talk Harry out of; Harry, Ron, and Hermione reach the appointed spot, but find Draco absent and the caretaker alerted to the presence of students out of bounds. While running away from him, they inadvertently enter the forbidden corridor, discovering that it contains a giant three-headed dog guarding a trapdoor. They narrowly escape, with Hermione expressing great disapproval about the situation arising at all.
Conflict with Hermione comes to a head on Halloween, when an unkind remark from Ron brings her to tears, locking herself in a bathroom for the afternoon. The Halloween Feast is then interrupted by the Defence Against the Dark Arts teacher, Professor Quirrell, warning of the presence of a troll in the castle. The students are sent back to their dormitories while the teachers search for the troll, but Harry and Ron, remembering that Hermione didn't come to the feast, go looking for her. They find the troll menacing the very bathroom that she's in, and after a dangerous scuffle, narrowly beat it by levitating its own club and knocking it out. Hermione becomes much warmer toward them in the aftermath, though she and Ron still bicker frequently. Harry also learns that Professor Snape went to the third-floor corridor during the attack, and was injured by the dog.
Harry plays his first Quidditch match, and proves to be a naturally talented flier. However, his broom starts misbehaving during the match, attempting to buck him off; Hermione sees Professor Snape staring directly at Harry without breaking eye contact, and distracts him by setting his robes on fire, after which Harry's broom returns to normal and he wins the match. In the aftermath, the trio visit Hagrid and tell him of their concerns about Professor Snape, including the possibility that he's trying to steal whatever "Fluffy" is guarding, but Hagrid insists that Professor Snape helped to set up the protections on the third floor, and would never do that.
Harry and Ron stay at the castle over Christmas, and Harry receives an Invisibility Cloak as an anonymous gift, with a note that it belonged to his father. He uses it to explore the castle at night, and discovers the Mirror of Erised, which shows the user their deepest desires; for him, that means seeing his parents standing by him. Headmaster Dumbledore later finds him staring into it, and warns that the mirror is dangerous and will soon be moved to a new location.
Putting together Hagrid's dropped remarks and other information, Harry and Hermione deduce that the object on the third floor is likely to be the Philosopher's Stone, which can transmute any metal into gold, and can produce the Elixir of Life that will make a person immortal. Harry also overhears Professor Snape threatening Professor Quirrell and asking him what he has found out about the protections.
In Spring, Ron discovers that Hagrid has obtained a dragon egg, and is planning to hatch and raise it in secret. The three of them are able to talk Hagrid into letting Ron's brother Charlie, a professional dragon handler, take the young dragon after it hatches; the handover works, but Harry and Hermione are caught out of bounds, along with Draco, who was trying to report them, and Neville, who was trying to warn them about Draco. All of them are sent into the Forbidden Forest at night with Hagrid, as detention, where they look for the source of recent attacks on the school unicorn herd. Harry comes across a cloaked figure drinking the blood of a freshly killed unicorn, and is narrowly rescued by a centaur, who informs him that unicorn blood can keep a person alive at the cost of inflicting a terrible curse upon them; he realises that the most likely candidate for taking such an action is Voldemort, and concludes that Snape is trying to steal the Stone in order to return Voldemort to full life.
When it turns out that Hagrid has unthinkingly told a stranger about how to get past Fluffy safely, the trio approaches their head of house, Professor McGonagall, to tell her of their suspicions, but she is dismissive of the idea that any staff member could or would try to steal the Stone. However, in the process, she reveals that Professor Dumbledore has been called away from the school; Harry assumes that this will be the window of opportunity for a thief, and resolves to challenge the protections himself to stop them. Ron and Hermione are reluctant but choose to help rather than stand aside. Neville tries to stop them from going, as they would be breaking rules, but Hermione disables him with a body-binding spell.
The three of them fight and puzzle their way past Fluffy, a large Devil's Snare plant, a locked door in a room full of flying keys, a giant chessboard, and a logic puzzle. In the process, Ron is knocked out by a chess piece, and Hermione is obliged to go back when there is only enough fire resistance potion for one person. Harry reaches the final room of the gauntlet, and finds not Professor Snape, but Professor Quirrell, attempting to retrieve the Stone from the Mirror of Erised. Quirrell reveals that Voldemort is parasitically attached to the back of his head, and is controlling his actions; Voldemort commands him to use Harry to retrieve the Stone, and upon looking into the Mirror, Harry feels the Stone appear in his pocket, but when Quirrell seizes him, the contact burns and blisters Quirrell's hands. Harry is knocked out, but Quirrell is disabled by the burning long enough for Professor Dumbledore to arrive and intervene. Voldemort's shade abandons Quirrell, who dies, and Harry awakens later in the Hospital Wing, where Dumbledore praises him for his actions and informs him that the Stone has been destroyed and Voldemort banished for now.
