Out on the beach, the kids are preparing to break into Bellatrix Lestrange's vault. Hermione has taken Polyjuice Potion to transform into Bellatrix, Ron is wearing a disguise, and Harry is carrying Griphook on his back under the invisibility cloak.
They apparate to Gringotts, and Hermione adjusts to pretending to being the nasty Bellatrix (it does not come naturally to her).
They enter the bank and head toward the tellers.
When Hermione tries to get the tellers to let her into Bellatrix's vault, they insist that she present her wand.
Griphook whispers that the tellers are suspicious. He can tell that they've been warned about an imposter coming.
From under the invisibility cloak, Harry uses the Imperius Curse on the teller, and suddenly they're on their way to the vault. Whoa, Harry's using Unforgivable Curses now? He really must be desperate to get that Horcrux.
In the cart down to the vault, they pass under some kind of magical waterfall, which apparently washes away all enchantments. Uh-oh.
Yep, that's right—suddenly Hermione and Ron look like themselves again. Oh, and they're all dumped out of the cart and several feet down to a hard concrete floor—apparently, once the enchantments were broken, the cart itself realized the kids shouldn't be there.
Luckily, some quick magic on Hermione's part prevents them all from going splat.
The Gringotts representative who has been accompanying them down to the vault is suddenly angry, when he realizes who they are (or aren't), until they Imperio him again.
Then, the kids hear an ominous noise, and it turns out to be a dragon. They keep a dragon beneath Gringotts. This can't be a good sign.
Also not good: the dragon does not look happy.
However, Griphook and the teller start shaking some things that make noise, and that scares the dragon. Apparently, he's been conditioned to expect pain when that noise happens. How sad.
They get past the dragon and enter the vault.
Once in there, they have a new set of problems to deal with. It seems there's some kind of charm on the treasure that makes it multiply when touched.
So, they're getting buried by fake treasure.
It's a total gong show, but Griphook manages to find what they're looking for: a gold cup that Harry believes is one of Voldemort's Horcruxes.
Victory, right? Well, not so fast: the goblin demands that Harry give him the sword before he'll hand the cup over.
They make the exchange, but then the goblin says he's peacing out. He promised to get them in there, but he didn't say anything about getting them out. Oh, dirty play, Griphook.
To make matters worse, other wizards have arrived to deal with the intruders.
So, just to keep score: the kids have been discovered as imposters, they no longer hold the item (the sword) that would destroy the Horcrux they just found, and they've lost their guide to getting in and out of Gringotts. We can't speak for you, but our hearts can't take all this stress.
Luckily, the kids think fast and find a solution: the dragon. Hermione, Ron, and Harry get on the beast's back and use him to escape.
The dragon is clearly very happy to be free, and once he bursts out of Gringotts, he books out far, far away from the bank with the kids still on his back.
When they're over a lake, the kids jump off. As they enter the water, Harry seems to see Voldemort's thoughts.