Confused by Harry Potter

Hi all. Today's post doesn't have anything to do with cruising, instead it's a question that's been bugging me for the last few days and I was hoping one of my readers might be able to help me.
Being the decent gent that I am I took my wife out to see the last Harry Potter movie recently. She's a massive fan and has been looking forward to seeing it since she saw the previous film.
I haven't really seen many of the movies, and this one was part two and I'd only seen half of the first one so perhaps my confusion is understandable.
Here's my question........