Harry and Hermione and Ron suspect there's a Horcrux in Bellatrix Lestrange's vault. And then they gotta try and find it without anyone recognizing them.
Harry Potter and the Deathly Hallows Part 2: Disguises
At the end of Hallows Part 1, there's a shot of this hair falling of Bellatrix Lestrange's head. And then at the beginning of part 2 we realize she still got the hair. That she can use it and polyjuice form. Hermione takes polyjuice potion to become Bellatrix. So she can break into Gringotts bank.
How do I look? Hideous.
And Harry's under the invisibility cloak. And Ron's just disguised. I quite enjoyed all those scenes where we were all kind of disguised. There's a full beard and they darkened my eyebrows. They just had all these gothic kind of robes. I walked on the set and people that I've known for like seven years just walked past me. Didn't have a clue who I was. No, I didn't actually recognize you at first. I thought that a Death Eater had walked on.
Madame Lestrange. Good morning. Good morning? You're Bellatrix Lestrange. Not some dewy-eyed schoolgirl!