Harry Potter and the Dealthy Hallows is the seventh and final book in J.K. Rowlings Harry Potter series. Voldemort is continuing to accumulate power and it is up to Harry, Ron, and Hermoine to find the remaining Horcruxes to defeat him once and for all. When the Death Eaters descend upon Hogwarts, it leads to a battle that will affect the future of the wizarding world forever.
Their plan is simple: Go with Griphook with Hermione disguised as Bellatrix Lestrange in order to access her vault. As Harry stole Bellatrix's wand during their tussle at Malfoy Mansion, they have her wand and even got some of her hair for use in Polyjuice Potion.
When they Apparate into the Leaky Cauldron they’re surprised to see how bad Diagon Alley looks. There are many more shops dealing in the Dark Arts, and most of the nice ones have closed down.
Their plan goes reasonably well. Hermione makes a very convincing Bellatrix and with only a few snags, and Griphook manages to get them down to her vault. It’s guarded by a half-blind dragon, but they get past that obstacle fairly easily thanks to Griphook.
Suddenly things start to fall apart. They’re discovered to be imposters and the treasure in the vault starts multiplying every time it’s touched. Harry manages to spot what they came for: Hufflepuff’s cup, which he is sure is a Horcrux. He just manages to get it before they’re all crushed to death. Griphook escapes with the sword,and Harry, Hermione, and Ron manage to get back out of the bank on the back of the half-blind dragon.