Harry Potter is a seemingly ordinary boy, living with his hostile relatives, the Dursleys in Surrey. On his eleventh birthday, Harry learns from a mysterious stranger, Rubeus Hagrid, that he is actually a wizard, famous in the Wizarding World for surviving an attack by the evil Lord Voldemort when Harry was only a baby. Voldemort killed Harry's parents, but his attack on Harry rebounded, leaving only a lightning-bolt scar on Harry's forehead and rendering Voldemort powerless. Hagrid reveals to Harry that he has been invited to attend Hogwarts School of Witchcraft and Wizardry. After buying his school supplies from the hidden London street, Diagon Alley, Harry boards the train to Hogwarts via the concealed Platform 9¾ in King's Cross Station.
The Minister of Magic, Rufus Scrimgeour, addresses the wizarding media, stating that the Ministry would remain strong even as Lord Voldemort gains strength. Harry, Ron and Hermione prepare for a journey to find and destroy Voldemort's Horcruxes, with Harry watching Dursleys depart and Hermione wiping her parent's memories of her.
Harry Potter is forced to defend himself against charges of using magic while underage, and in the presence of his Muggle cousin Dudley, after the two are attacked by Dementors. The Order of the Phoenix, a secret organisation founded by Albus Dumbledore, inform the now pending expulsion Harry that the Ministry of Magic is oblivious to Lord Voldemort's return; under the Ministry's influence, The Daily Prophet has launched a smear campaign towards Harry and Dumbledore following Harry's encounter with Voldemort at the end of the previous year. This encounter had a huge psychological effect on Harry – he has nightmares not only about what happened in the graveyard but also about the Department of Mysteries at the Ministry of Magic. While at the Order's headquarters, Harry's godfather, Sirius Black, mentions that Voldemort is after an object which he did not have last time.
Lord Voldemort is tightening his grip on both the wizarding and Muggle worlds and has chosen Draco Malfoy to carry out a secret mission. Severus Snape makes an Unbreakable Vow with Draco's mother, Narcissa, to protect Draco and fulfill the assignment if he fails.
Harry Potter dreams of Frank Bryce, who is killed after overhearing Lord Voldemort discussing plans with Peter "Wormtail" Pettigrew and Barty Crouch Jr. At the Quidditch World Cup, Death Eaters terrorise the spectators, and Crouch Jr. summons the Dark Mark, otherwise known as the curse "Morsmordre".
Harry Potter spends the summer at the Dursleys' house without receiving letters from his Hogwarts friends. He is sent to his room by The Dursleys to avoid embarassing them in front of Uncle Vernon's friends, who are coming over as guests.
Harry Potter, now aged 13, has been spending another dissatisfying summer at Privet Drive. When Uncle Vernon's sister, Marge, insults Harry's parents, he becomes angry and accidentally causes her to inflate and float away. Harry flees with his luggage, fed up with his life with the Dursleys. The Knight Bus delivers Harry to the Leaky Cauldron, where he is forgiven by Minister of Magic Cornelius Fudge for using magic outside of Hogwarts. After reuniting with his best friends Ron and Hermione, Harry learns that Sirius Black, a convicted supporter of the dark wizard Voldemort, who murdered Harry's parents, has escaped Azkaban prison, intending to kill Harry.