Griphook agrees to help them break into Bellatrix Lestrange’s Gringotts vault, but he demands the Sword of Gryffindor as payment. This puts Harry and his friends in a bind, because if they refuse, they’ll never get into the vault to look for a Horcrux, but if they give up the sword, they’ll have no way to destroy any Horcrux they find. Harry decides to trick the goblin, telling him he can have the sword after they break into the vault, but not specifying how long after. Feeling somewhat guilty, Harry gives his promise to Griphook, and for several weeks they plan the break-in.
Lupin arrives at the cottage with the news that Tonks has had her baby. He asks Harry to be the godfather, and Harry agrees.
Before Harry and the others embark on their mission, Bill takes Harry aside. He does not know what Harry is planning to do or how Griphook is involved, but he warns Harry to be careful of goblins. He says that goblins are deeply distrustful of wizards, believing that wizards do not respect agreements involving treasure and tend to trample on goblin rights. He explains that goblins believe manufactured items belong to the maker, and that ownership of goblin-made goods should not pass from wizard to wizard but should revert to the goblins after the first owner’s death. He warns Harry of the dangers of reneging on a deal with a goblin.
To break into Gringotts, Hermione disguises herself as Bellatrix Lestrange and changes Ron’s appearance so he’s unrecognizable. With Harry and Griphook under the Invisibility Cloak, the four go to Diagon Alley, where they see witches and wizards begging in the streets, deprived of their wands by the Ministry.
A Death Eater named Travers stops Hermione/Bellatrix, noting that he’d heard she’d been confined to her house and lost her wand, but Hermione dismisses his questions contemptuously, in a good imitation of Bellatrix’s manner. Unfortunately, Travers is going to Gringotts too, and they enter the bank together.
The first security obstacle they face is Probity Probes—rods that detect the presence of Concealment spells and magical items. Harry sneaks up in his cloak and zaps the guards working the probes with spells of Confusion.
At the customer service counter, Hermione asks to be admitted to Bellatrix’s vault, and a goblin asks her for identification. When the goblin says her wand will suffice, Harry realizes that they must know Bellatrix lost her wand and must be expecting an impostor, so he uses the Imperius curse to control the goblin’s mind. The goblin compliments her on her new wand, which makes Travers suspicious, so Harry controls him as well.
The entire party, led by the mind-controlled goblin, gets into a rail cart and travels deep into the vaults. Harry curses himself for the strategy they’ve adopted, realizing that the Death Eaters know all about who stole Bellatrix’s wand, and that posing as Bellatrix has already brought them too much scrutiny and attention. When the cart passes through a waterfall and all of their Disguising spells are undone, Griphook tells them that the Gringotts employees have set up defenses indicating that they know impostors are present.
A dragon blocks the passageway to the vault, but Griphook shakes metal instruments called Clankers, which the dragon has been trained to fear, and it backs up. The mind-controlled goblin places his palm to the door of the vault, and it opens.
Harry knows from his conversations with Dumbledore that if a Horcrux is in the vault, it must either be the Hufflepuff cup or else an unknown object, so they have no choice but to look for the cup. Unfortunately, whenever they touch anything inside the vault, it burns them and then multiplies into myriad worthless copies, so that if they continue touching items in the vault, it will eventually fill and crush them. They try not to touch anything as they search, but this proves impossible.
Finally, they see the cup sitting high up out of reach. The dragon roars outside the door, and the heat from the multiplied treasure is overwhelming. Hermione Levitates Harry toward the cup, but he knocks over a suit of armor, and they begin to be buried in hot objects. Harry uses the sword to skewer the cup through a handle as Griphook sinks beneath the burning treasure. Harry stops to save him, letting go of the sword, and Griphook seizes the sword, flinging the cup into the air. Harry realizes that Griphook never believed Harry would keep his word, but he manages to catch the cup again as Griphook disappears.
A crowd of goblins appears in the passage, there to apprehend Harry and company. Harry uses his wand to free the chained dragon, then the three get on the dragon’s back and ride it through the tunnel, eventually emerging in the bank lobby, exiting through the door, and flying off into the sky above Diagon Alley.
The dragon flies far off into the countryside, finally flying lower over a mountainous lake. Harry and friends decide to jump off into the lake, and make their way, bruised, burned, and battered, to the shore, the cup safely in their grasp.
Harry has a vision in which he not only sees out of Voldemort’s eyes but reads his thoughts. Voldemort is questioning a goblin about the break-in, and when told that Harry Potter was the thief and that the cup was the item stolen, he flies into a rage and kills the goblin and all the wizards who don’t flee fast enough, using the Elder Wand. Voldemort is not yet aware that Harry knows about his Horcruxes and is destroying them, because he does not feel anything when they are destroyed. Now that his cup Horcrux has been stolen, it finally occurs to him that Harry might be after his Horcruxes, and that Dumbledore might have given Harry the means to find them out. He resolves to check on his ring and his locket to see that they’re safe, and to keep Nagini the snake (which is itself a Horcrux) beside him at all times. Finally, he will check on the last and safest Horcrux, which is at Hogwarts.
Harry relays this information to his friends. They know they have very limited time, because Voldemort will discover that his ring and locket are gone within a matter of hours, and may move the final Horcrux to a new hiding place. On a more positive note, they now know the final Horcrux is at Hogwarts, so they set off for the village of Hogsmeade.
Now that Harry has made his decision and committed himself to finishing the quest, the novel starts to move more quickly to its conclusion, and in three chapters the trio pulls off their most audacious mission yet, breaking into and out of the famously well-protected Gringotts bank. When Harry was introduced to Gringotts in the first novel, something as foolhardy as breaking into a vault was probably the furthest thing from his, or the reader’s mind.
Harry’s qualms about lying to the goblin, and Bill’s warning about playing fast and loose in deals with goblins, are both examples of foreshadowing. We know that the implicit conflict between Griphook and Harry over the sword will eventually break out into the open, and Harry will have to find a new way to destroy Horcruxes.
In the heist sequence, we see the results of the Ministry’s activities, as wandless witches and wizards are reduced to begging in the gutter. The suspense of the break-in is heightened by its being narrated from Harry’s point of view, even though it is Hermione who is under the most pressure to perform.
The image of Voldemort killing his followers brings our attention back to Voldemort as the central threat. Now that the conflicts in the middle of the book, between Harry and his friends and between Harry and himself, have either been resolved or receded into the background, the novel moves into its final phase. Voldemort discovers the true nature of Harry’s quest, and the quest brings Harry and his friends directly into confrontation with Voldemort.