"Are you a math fan, then?"

"I like most subjects. Math's one of them, but it doesn't come up much in my work and it hasn't rotated into the position of my favorite hobby yet. I imagine it will. I'm immortal."

"That must be very handy," says Libby.

"It is! We like it. It's just about Mama's favorite part of being a vampire, and she's extra immortal - she's been set on fire twice."

"What's your mother like, anyway? I'm still having trouble picturing this kindhearted world dictator." She waves the relevant pamphlet. "Photographic evidence notwithstanding; I mean in a more abstract way."

"Oh, she's very smart, and kind of paranoid but people did keep trying to kill her for the longest time, and she loves me and my dad to bits, and she's careful about being ethical with all her power - she put my grandpa Carlisle in charge of the ethics of the R&D department and if you knew my grandpa Carlisle you'd know that means she takes not being evil very seriously. She doesn't like being interrupted. She raised me by herself for five years when we thought my dad was dead and she was the most devoted mama anyone could ask for. She's got a lot of... psychological resilience, I guess? Most vampires who thought their mates were dead would just fall completely apart - they'd go for a futile, suicidal attempt at revenge or turn into apathetic zombie-types or go outright insane. Mama managed to function and bring me up to maturity. She cares about knowing where all her mental moving parts are and making sure they don't break or go the wrong way."

"She sounds like a hell of a mom," says Libby. "I approve. And now I kind of want to meet your grandpa Carlisle."

"He's been here one time," Elspeth says. "He didn't know what to make of it. I don't think he liked it very much. He might have seen a version of somebody he didn't like the look of?" she guesses.

"Too bad," says Libby. "Guess I missed my chance. Unless it scoops him up again out of spite; I hear it's been known to."

"He'd probably politely tell it he didn't appreciate that and then leave," Elspeth predicts.

"I definitely want to meet your grandpa Carlisle."

Elspeth shrugs. "I'm allowed to bring people - well, humans who don't have particularly threatening magical powers - home with me, if you want."

"What's a particularly threatening magical power?"

"If you could get through me or Jake in a serious - however unlikely - attempt to do me any harm, that's the relevant threshold," Elspeth says. "Mama's convinced that Milliways is safe, but all bets are off in a world. Other relevant people are tougher to hurt than I am."

"I think you're safe," says Libby, which has the dual benefit of being perfectly true while concealing the actual answer to that question.

"Do you actually want to come home with me or is this hypothetical? Because I have to try my check if you do."

"It's mostly hypothetical. I'd probably want to pick a better time. What's the check?"

"I mentioned that I can learn things about other people by seeing what makes sense to say. It doesn't catch everything, but what it catches is unrelated enough to what people want caught that Mama considers it a fine first-pass check - you'd still have to get past my dad or Maggie to stay welcome in our world for any length of time."

"How exactly does that work?" she asks interestedly.

Libby laughs. "Would the same method work to tell me how much danger I'd be in, in your world?"

"Sure," Elspeth says. "Assuming that you're really interested in being informed about that."

"Definitely," she says. "And I know someone who's even more so. If I ever decide to visit, maybe I'll drag her in here for a chat."

"You would be... exactly as safe in my world as anywhere else," Elspeth says. "...Why is that the most informative way to put that?"

"Informative and very reassuring!" says Libby. "I guess I should explain. My world has some people with native powers not unlike witchcraft, and my aunt's is a personal shield that she keeps pointed at me because she's an incorrigible worrier. Proof against anything from bug bites to neutron bombs, if you believe her."