At Malfoy Manor, Snape explains that the Order of the Phoenix plans to move Harry in a few days. Voldemort asks Lucius Malfoy for his wand—he needs it to kill Harry. At the Dursleys' house, Harry reads an obituary for Dumbledore and learns that Rita Skeeter will publish a biography on Dumbledore. Harry believes he sees Dumbledore's eye in a piece of enchanted mirror. The Order arrives for Harry and explains the plan: six of them will transform into Harry using Polyjuice Potion, and each will go to a different safe house. However, once the plan is in action, Death Eaters surround Harry and kill Hedwig, and Hagrid's motorcycle crashes. George loses an ear and Mad-Eye Moody dies. Harry sees a vision of Voldemort torturing the wandmaker Ollivander for giving him bad information.
Over the next week, Mrs. Weasley keeps Harry, Ron, and Hermione so busy with preparations for Bill and Fleur's wedding that they don't have a chance to plan their hunt for the Horcruxes. Though Harry tries to convince Ron and Hermione to not come with him, they insist on coming. Scrimgeour, the Minister of Magic, stops by to give the trio what Dumbledore left them in his will: The Tales of Beedle the Bard for Hermione; his Deluminator for Ron; and the first Snitch Harry caught for Harry. Dumbledore intended for Harry to receive the sword of Gryffindor, but Scrimgeour refuses to pass it on.
Harry attends the wedding in disguise as a Weasley cousin. He reunites with Viktor Krum, who's upset that Luna Lovegood's father, Xenophilius, is wearing the evil wizard Grindelwald's symbol, and gets involved in an argument between Elphias Doge and Auntie Muriel about Dumbledore. Muriel insists that Dumbledore's past is sketchy. A Patronus arrives and says that Voldemort took over the Ministry. Hermione quickly Disapparates with Harry and Ron to the middle of London. Two Death Eaters attack them, but the trio manages to escape to number twelve, Grimmauld Place.
At Grimmauld Place the next morning, Harry discovers that Sirius's brother, Regulus Arcturus Black, might be the R.A.B. from the locket. He summons Kreacher, who confirms this: Regulus tried to undermine Voldemort. Harry sends Kreacher to find Mundungus, who stole the real Horcrux. Lupin stops by a while later and offers to help the trio, but Harry declines. Kreacher returns with Mundungus soon after, who admits that Dolores Umbridge stole the locket. The trio begin planning to infiltrate the Ministry and steal it back.
Using Polyjuice Potion to disguise themselves as employees, the trio sneak into the Ministry of Magic, where Harry discovers that Moody's magical eye being used to spy on employees. He steals it and then Stuns Umbridge in the middle of court proceedings trying Muggle-borns. He and Hermione take the locket, help the Muggle-borns awaiting trial to escape, and then Disapparate for Grimmauld Place with Ron—but a Death Eater holds on and comes with them, and he sees Grimmauld Place. Hermione whisks them away to a deserted field, and they begin camping and moving through the countryside. Harry insists that they wear the locket for safekeeping, even though it makes the wearer unusually irritable. It affects Ron the worst. Harry sees inn a vision that Voldemort is chasing a golden-haired man who stole something from the wandmaker Gregorovitch.
One rainy evening, Harry, Ron, and Hermione hear people coming. They listen as Ted Tonks, Dirk Cresswell, Dean Thomas, and the goblins Griphook and Gornuk discuss that several students, including Ginny, tried to steal the sword of Gryffindor from Snape, who is now the Hogwarts headmaster. The goblins giggle that the sword at Hogwarts is a fake. Hermione pulls out the portrait of Phineas Nigellus, which she stole from Grimmauld Place, to ask him about things at Hogwarts. He tells her that Dumbledore last used the sword to destroy a ring, and Harry and Hermione are thrilled to have figured out that Dumbledore left Harry the sword so he could destroy Horcruxes. Ron, however, is unimpressed and in a fit of rage, he leaves. Hermione cries for days.
Around Christmas, Hermione agrees to go to Godric's Hollow. Disguise as Muggles, she and Harry find the graves of Kendra and Ariana Dumbledore, as well as Lily and James's graves. As they leave town, old Bathilda Bagshot stops them and invites them into her home, which reeks. Harry finds a photograph of the golden-haired thief and follows Bathilda upstairs, asking for the sword. To his horror, the snake Nagini uncoils grotesquely out of Bathilda's body and Hermione barely manages to get them out alive. Harry finds himself in Voldemort's mind, reliving the night that Voldemort killed his parents. When he wakes, he learns that his wand broke in the scuffle, and Hermione reveals that she stole Skeeter's biography of Dumbledore from Bathilda. This allows them to identify the thief as Grindelwald, a friend of Dumbledore's. Harry is disturbed to learn that Dumbledore flirted with a plan to dominate over Muggles as a young man.
A few nights later, while Harry is keeping watch, a silvery doe approaches and leads him to a frozen pool. The sword of Gryffindor is at the bottom. Harry strips and dives, but the Horcrux tries to strangle him. He comes to on the bank: Ron saved him and got the sword. Harry lets Ron stab the Horcrux, which voices all of Ron's greatest fears before it dies. Hermione is incensed to see Ron again. Ron explains that the Deluminator led him back; that there are people called Snatchers out looking for wanted people; and that saying Voldemort's name alerts the Ministry. He has an extra wand for Harry.
Hermione, after noticing the strange symbol in The Tales of Beedle the Bard and in Dumbledore's biography, insists they visit Xenophilius to ask him about it. He nervously tells them that it's the mark of the Deathly Hallows, which are three objects—the Elder Wand, the Resurrection Stone, and the Invisibility Cloak—that make a person master of death. He also reveals that the Death Eaters kidnapped Luna, and tries to turn in the trio. They escape, and Harry becomes obsessed with finding the Hallows.
One evening, Harry accidentally utters Voldemort's name and Snatchers, including Fenrir Greyback, arrive. Hermione curses Harry's face so he's unrecognizable, but Greyback sees through it. He takes his captives, including Dean and Griphook, to Malfoy Manor. There, Bellatrix Lestrange is terrified and incensed to see the sword of Gryffindor, which is supposed to be in her Gringotts vault. She tortures Hermione, and Harry asks Griphook to identify the sword as a fake. Harry sees Dumbledore's eye in the mirror fragment and asks for help. Dobby appears a minute later and begins to Disapparate with Luna and Ollivander, who are imprisoned in the cellar. Harry manages to steal wands from Draco and Disapparate, but Bellatrix throws a knife that hits Dobby. Dobby dies in Harry's arms outside of Bill and Fleur's cottage, and Harry digs the grave by hand. Harry now knows what Voldemort is after—the Elder Wand, which belonged to Dumbledore—but he decides to dedicate himself to going after the Horcruxes instead.
With Griphook, the trio begins plotting to break into the Lestranges' Gringotts vault by having Hermione impersonate Bellatrix. They agree to give Griphook the sword in exchange, but at a later date. The plan goes reasonably well; they manage to steal another Horcrux and escape on the blind dragon that guards the vaults, though Griphook runs away with the sword. When they land, however, Harry sees that Voldemort knows that they're targeting his Horcruxes. As Voldemort thinks that there's one at Hogwarts, Harry insists they have to go to Hogwarts before Voldemort gets there. They Apparate into Hogsmeade, which sets off alarms, but Aberforth Dumbledore, the barman at the Hog's Head and Dumbledore's brother, saves them. He tells them the truth about Ariana: that she repressed her magic after being abused by Muggle boys, and that Dumbledore felt burdened by her. He encourages Harry to abandon Dumbledore's plan, but Harry insists on getting into Hogwarts. Aberforth agrees and a portrait of Ariana fetches Neville. Neville and other students have been hiding in the Room of Requirement and are thrilled to fight Snape. Harry grudgingly agrees to let them help as he looks for Ravenclaw's diadem, which he believes is the final Horcrux.
The Death Eater Alecto Carrow catches Harry in the Ravenclaw common room, but Luna and McGonagall save him. McGonagall, Sprout, and Flitwick duel with Snape, who leaves to join Voldemort, and then they begin to secure the school. Harry confirms that the diadem is the final Horcrux while Ron and Hermione sneak into the Chamber of Secrets and destroy the cup Horcrux with a basilisk fang. They all go into the iteration of the Room of Requirement where objects are hidden, but Draco, Crabbe, and Goyle interrupt them. They find the diadem, but Crabbe conjures Fiendfyre—which destroys the Horcrux—but dies in the inferno. Members of the Order of the Phoenix arrive and the battle begins. Harry sees Fred die and Hagrid be carried into the Forbidden Forest by giant spiders. Voldemort is with Nagini in the Shrieking Shack, and Harry sneaks toward him in the hope of killing Nagini, who's also a Horcrux. Instead, he watches Voldemort murder Snape and then leave. Snape gives Harry memories before he dies.
Harry views the memories in the Pensieve. He learns that Snape has been working for Dumbledore the entire time because he's loved Lily since they were children, and Harry learns that Harry himself is the final Horcrux and needs to die, willingly, at Voldemort's hand. Harry discovers the Resurrection Stone in the Snitch and conjures his parents, Lupin, who died in the battle, and Sirius. Voldemort kills Harry, and Harry finds himself in a dreamy, white space, where Dumbledore is waiting for him. Dumbledore praises Harry, says that Harry is still alive, and explains how he orchestrated Harry's journey. Harry realizes that because Draco Disarmed Dumbledore before Dumbledore died, and because Harry then Disarmed Draco, Harry is the true master of the Elder Wand.
Harry chooses to return to life. He pretends to be dead, and Narcissa Malfoy, wanting to get to Hogwarts and find Draco, lies and says that he's dead. Hagrid carries Harry out of the forest. Voldemort tries to torture Neville by putting the Sorting Hat on his head and setting him on fire, but his curses don't function properly—Neville breaks free and kills Nagini. Mrs. Weasley kills Bellatrix, while Harry gives Voldemort the opportunity to repent. Harry responds to Voldemort's killing curse with a Disarming spell, and the killing curse backfires. Voldemort dies. Harry uses the Elder Wand to repair his original wand.
Nineteen years later, Harry and Ginny put their son, Albus Severus, on the Hogwarts Express. Albus is concerned he's going to end up in Slytherin, but Harry reminds his son that one of the bravest headmasters ever, Severus Snape, was from Slytherin.