Harry Potter and the Philosopher's Stone tells the tale of Harry, an ordinary boy who discovers he is not so ordinary after all; not only is he a wizard, he is also the target of the evil Lord Voldemort, who tried to kill Harry when he was a baby. As he makes his way through his first year at Hogwarts School of Witchcraft and Wizardry, Harry must again confront Voldemort with the help of his new friends. Major themes include good versus evil and the journey from childhood to adulthood.
The most evil and powerful dark wizard in history, Lord Voldemort, murdered married couple James and Lily Potter but mysteriously disappeared after failing to kill their infant son, Harry. While the wizarding world celebrates Voldemort's apparent downfall, Professor Dumbledore, Professor McGonagall and half-giant Rubeus Hagrid place the one-year-old orphan in the care of his surly and cold Muggle uncle and aunt, Vernon and Petunia Dursley and their spoilt and bullying son, Dudley.
For ten years, living at number Four Privet Drive, Harry is treated by the Dursleys more like a servant than a member of the family and is forced to live in a cupboard under the stairs. Shortly before his eleventh birthday, a series of letters addressed to Harry arrive, but Uncle Vernon Dursley destroys them before Harry can read them, leading to an influx of more and more letters. To evade the pursuit of these letters, Vernon first takes the family to a hotel, but when the letters arrive there too, he hires a boat out to a hut on a small island.
It is Harry's eleventh birthday and at midnight, Hagrid bursts through the door to deliver the letter and to tell Harry what the Dursleys have kept from him: Harry is a wizard and has been accepted into Hogwarts School of Witchcraft and Wizardry. Hagrid takes Harry to a hidden London street called Diagon Alley, where he is surprised to discover how famous he is among the witches and wizards, who refer to him as "the boy who lived." He also finds that his parents' inheritance is waiting for him at Gringotts Wizarding Bank. Guided by Hagrid, he buys the equipment he will need for his first year at Hogwarts and as a birthday gift Harry receives a pet owl from Hagrid.
A month later, Harry leaves the Dursleys' home to catch the Hogwarts Express from King's Cross railway station. There he meets the Weasley family, who show him how to pass through the magic wall to Platform 9¾, where the train that will take them to Hogwarts is waiting. While on the train, Harry meets two fellow first years, Ron Weasley, who immediately becomes his friend, and Hermione Granger, with whom the ice is a bit slower to break. Harry also makes an enemy of yet another first-year, Draco Malfoy. Draco offers to advise Harry, but Harry dislikes Draco for his arrogance and prejudice and rejects his offer of "friendship".
At Hogwarts, the first-years are assigned by the magical Sorting Hat to houses that best suit their personalities. While Harry is being sorted, the Hat suggests that he be placed into Slytherin which is known to house potential dark witches and wizards, but when Harry objects, the Hat sends him to Gryffindor. Ron and Hermione are also sorted into Gryffindor. Draco is sorted into Slytherin, like his whole family before him.
Harry starts classes at Hogwarts School, with lessons including Transfiguration with Head of Gryffindor, Minerva McGonagall, Herbology with Head of Hufflepuff, Pomona Sprout, Charms with Head of Ravenclaw Filius Flitwick, and Defence Against the Dark Arts with Quirinus Quirrell. Harry's least favourite class is Potions, taught by Severus Snape, the vindictive Head of Slytherin who seems to loathe Harry. Harry, Ron, and Hermione become far more interested by extracurricular matters within and outside of the school, particularly after they discover that a huge three-headed dog is standing guard over a trapdoor in a forbidden corridor. They also become suspicious of Snape's behaviour and become convinced that he is looking for ways to get past the trapdoor.
Harry discovers an innate talent for flying on broomsticks and is appointed as Seeker on his House’s Quidditch team, a wizards's sport played in the air. His first game goes well until his broomstick wobbles in mid-air and almost throws him off. Ron and Hermione suspect foul play from Snape, whom they saw behaving oddly. For Christmas, Harry receives an invisibility cloak from an anonymous source and begins exploring the school at night and investigating the hidden object further. He discovers the Mirror of Erised, in which the viewer sees his deepest desires becoming true.
Thanks to an indiscretion from Hagrid, Harry and his friends work out that the object kept at the school is a Philosopher's Stone, made by an old friend of Dumbledore named Nicolas Flamel. Harry is also informed by a centaur he meets in the forest that a plot to steal the Philosopher’s Stone is being orchestrated by none other than Voldemort himself, who would use it to be restored to his body and come back to power. When Dumbledore is lured from Hogwarts under false pretences, Harry and his friends fear that the theft is imminent and descend through the trapdoor themselves.
They encounter a series of obstacles, each of which requires unique skills possessed by one of the three, and one of which requires Ron to sacrifice himself in a life-sized game of wizard's chess. In the final room, Harry, now alone, finds Quirrell, who admits that he had tried to kill Harry at his Quidditch match against Slytherin. He also admits that he let a troll into Hogwarts. Snape had been trying to protect Harry all along rather than to kill him, and his suspicious behaviour came from his own suspicions about Quirrell.
Quirrell is one of Voldemort's followers, and is now partly possessed by him: Voldemort's face has sprouted on the back of his own head, hidden by his turban. Voldemort needs Harry's help to get past the final obstacle: the Mirror of Erised, but when Quirrell tries to grab the Stone from Harry his contact proves lethal for Quirrell. Harry passes out and awakes in the school hospital, where Dumbledore explains to him that he survived because his mother sacrificed her life to protect him, and this left a powerful protective charm on him. Voldemort left Quirrell to die and is likely to return by some other means. The Stone has now been destroyed. The school year ends at the final feast, during which Gryffindor wins the House Cup. Harry returns to the Dursleys' for the summer holiday but does not tell them that under-age wizards are forbidden to use magic outside of Hogwarts.