Cool, then. She'll take history of the supernatural, on the grounds that she already knows archery and if she wants to know it better she can practice with Alex, and then more identifying demons.

Identifying demons has advice on shapeshifters and possession and various demon species that sometimes pass as human. You can do something like a DNA test to identify many kinds of demon, apparently. They've been building an encyclopedia of blood and tissue and hair and glowing ooze samples from crime scenes around the country, now that they know what to look for. There are demons with regenerating powers, and they're studying the regenerating heart tissue of one particularly dangerous species for possible medical applications.

History of the supernatural includes a guest lecture from a cheerful anthropologist who explains that humans and demons in some societies may have lived and worked together, and a lot of deciphering references in old books. Dracula is a real thing, apparently. 

One of the lecturers takes Karen aside after the second day. "Hey! I have a question, do you have a minute?"

"Sure, what can I do for you?"

"So, uh, this class usually includes a day covering the slayers. Most of them - well, all of them died in the line of duty, and mostly very young. If you'd like to skip the lecture, or read the notes in advance so it isn't surprising or upsetting, either of those things would be completely reasonable. The world's a better place now, you have more support than slayers used to, and better weapons... I don't think you should be scared or anything, it just seemed like it could be an upsetting lecture."

"Oh! That's really considerate, but I'm fine, actually? I can look at the notes anyway, but I sort of know about the dying part."

"Okay! It's up to you but I have a copy of the notes here if you decide you do want to read them."

"Sure, I can look at them. Thanks."

The notes are scattered up through the 20th century and pretty good from then forward. Slayers often don't make it to their eighteenth birthday and those that do have a tendency to die on it. There's one who made it to 22 before being killed in a New York subway by the same vampire that killed a different slayer a century earlier.

This is not terribly new information, but she reads it with interest anyway. She likes history.

She writes home to Azalea and Alex and Wishbone, summing up the cool parts of summer camp and some of the neat things she's learned and some of the potential friends she is potentially making. She tries to go light on the complaints, and resists the urge to leave some kind of secret code in Alex's letter that works out to 'everything is terrible, can't wait for Deathtrap School to be in session again'. It's not that bad. Her brain is screaming a little less this week.

She is to all appearances moderately enthusiastic when it's time for the slayer lecture.

The Slayer lecture is exactly as promised! There's grainy surveillance video of the fight in the New York subway. They stop before the part where the Slayer dies, which means it's mostly just a really cool fight. A lot of the kids look fairly upset on Karen's behalf. 

"Isn't the test of the Slayer's abilities, uh, murder?"

"Yes," says the lecturer. "Prosecutions are complicated, though, and the last six incidents have not been in the United States."

"Do other countries have organizations like this one?"

"I wouldn't know."

She cheerfully takes notes on all of this. There's really nothing to be upset about. Maybe it's the whole already-having-died-twice thing.

Invisible girl picks a name. It's Trace. "I think it sounds cool."

"It's nice! Trace."

"I'm gonna go back to the facility during the daytime and see if I can get down to the lower floors."

"Makes sense. You don't think they'll catch you?"

"No one ever thinks about me. And they didn't last time."

"Yeah. Be careful, though, they have to remember that they have an invisible camper."

"I'll be careful."

Then she'll just have to wait to hear back. She feels a tiny bit guilty about wanting to know what exactly they're doing down there, especially since she hasn't been taking on any of the risk of finding out on her own, but such is life.

Her cabinmates do not seem to feel similarly guilty. They stay up playing Twenty Questions and this time when the door opens they don't freak out. 

"Hi!" says Trace. "I made it into the elevators, but the lower floors have locked doors. I don't think they're offices, though. The doors were reinforced."

"Could just be how they build military installations."

"I guess."

          "But the doors on the first floor weren't reinforced?" said Callida. 

"Nah, those ones seemed like normal doors."

          "There's got to be a way to get in."

"I might try to steal a keycard but I don't want to get in trouble."

Karen, too, doesn't really relish the thought of getting in trouble. She told Alex she would be polite. She's pretty sure that breaking into people's offices is traditionally considered impolite.

It takes about a week for letters to get to Sunnydale and for replies to get to the camp. Azalea's is half a page long, which is really pretty impressive for her. The other half of the page is taken up by Connor's drawing of her leading troops into battle against an army of what she supposes are vampires, judging from the fangs. Wishbone's letter is ten pages of typed text, because he's just like that as a person. She reads it all the day it arrives. Halfway through the third page, inserted apparently at random between unrelated anecdotes about how he's spending his summer, there's a note. 

I find it very interesting that the government claims to be using the regenerative properties of T'kelt demons in modern biomedical research. T'kelt regeneration is magical in nature, and stops working the moment the source demon dies. I suppose someone could separate a piece of the T'kelt demon's body while it lived, and perhaps make use of the separated parts, but it would require periodically harvesting tissue from a living captive, and ensuring that the captive remained alive. I've often found T'kelt demons very rude, myself, but if humans have been doing vivisections then I suppose I find that a bit more understandable.

She doesn't give any patently obvious outward sign that this bothers her. Maybe she fidgets more. Maybe she sleeps worse that night. She has a half-formed thought in her head that refuses to quite come together, and it bothers her, but it won't go away.

"D'you think the lecture materials from last week are still in the camp somewhere?" she asks Trace, the next day, idly picking at her macaroni and cheese.

"I think Melissa carries them around. Don't you take notes?"

"Yeah, there's just this thing I sort of half-remember and I'm not sure if I have it in my notes correctly? And - I dunno, it's bugging me."