Bella is about to turn thirteen! This is exciting.
It gets a little chilly.
Maybe the sun is just not so high in the sky any more. Maybe there's more cloud cover.
(There's not more cloud cover.)
Bella is still standing up. She checks her wand grip.
She says, "I don't know if this is going to work."
And then she aims at the Dementor and snaps, "Expecto patronum."
That's not mist.
It's light, pouring out of her wandtip, and forming a very definite shape.
It's not an animal. It's a person, two arms and two legs, indeterminate sex, compact enough that it's not even necessarily a human but could be an elf or a goblin or a hag, its shifting glow and fog obscuring where it would have features. It's the idea of a person.
Bella keeps her wand raised, biting her lip so hard that she's starting to bleed, and her blindingly silver person warms the air and lifts the oppressive dark -
And it darts forward almost too quick to see, and its hand shoots towards the dementor as though to strangle the monster -
Which dissolves on contact.
Leaving a tattered cloak, falling into a heap at the feet of the glowing Patronus.
"They might ask the Azkaban Dementors. They have some way I don't understand of communicating with them, I don't know if other Dementors can tell what just happened to this one." She gestures at the cloak. "Speaking of which I don't know how to dispose of that."
"Crossing international borders is complicated and long trips require more packing. There are an estimated fifty wild dementors in the whole world - I think the one I killed must have followed us specifically, or it'd be too weird to find one again so soon - so there's maybe a handful in the States at any given time, and you fly fast but going a couple hundred miles an hour is still a day trip if we have to go to Denver, let alone Boston."
"Well, I'm in the eighth grade now, I can leave campus on weekends, let's see how long it takes to get to - oh, Santa Cruz? We can go over the water so nobody much will see me flying, that's allowed on brooms as long as you have plenty of altitude so it should be allowed on you. And get lunch and time our way back."
"Dementors are a death thing," says Bella. "Obviously people die other ways, almost all of the time, but Dementors are sort of - about death. Almost like how unicorns are about purity - except you aren't in magizoology - I don't know. Does that make sense though, that Dementors are about death, bad in the way death is?"
"I'm not sure what casting a regular Patronus is like so I don't know if my guesses about regular ones are right, but they're all animals except mine, mine's a person, mine is shaped like a kind of thing that can know what death is and that it's coming if it thinks about it. Thestrals and eagles and owls can't do that. I think a regular Patronus is saying 'not yet' - kind of -" She sticks her fingers in her ears, "la la la, I can't comprehend mortality, I am a happy cartoony creature!" - she puts her hands down. "And Dementors aren't death itself, they're just about it. You can stop thinking about one thing if you think about another thing hard enough, you can stop being scared if you think about happy things hard enough, regular Patronuses seem to me like they might be the magic version of that?"
Bella re-reads her musings, and says, "So that's most of what I think I'm doing. That and concentrating on how - I'm going to fix it. All of it. The Dementors first since I know how to do that now, but everything else too, I'm going to figure out how to live forever, because why shouldn't I, magic is real, and then I will fix everything else."
"I wasn't sure it was going to work," says Bella. "I thought about the Dementor a lot after we first saw it, though. What it looked like and how it made me feel and how I wanted to kill it. And once I was full up on chocolate - I didn't even eat that much of it - I felt kind of - like - like I was a critter it's a really bad idea to corner, does that make sense? You know how some kinds of animals won't attack you but if you hem them in you are not going to make it home intact - the Dementor sort of had me cornered, or Death did, or something, and that was a bad move. I'm rambling - just - it was the thing I thought of that seemed like might work. Especially based on what thoughts gave me mist when I was trying to do a regular Patronus."