He feels an open summons and lets it grab him -
"I think we fucked it up, Rayne."
"Gimme that," says the other one, reaching for the book.
"We did everything right," says the second boy, examining the open pages of the book and comparing a diagram there to the circle on the floor.
"I told you not to trust that fucking book," the first one grumbles. "Didn't I bloody tell you? Now look what we've done."
"Well, no use crying over spilled milk," says the second. "We got something." He addresses Cam. "We want you to clean our apartment."
"Ugh," says the first boy, rubbing his face with both hands. "Why do I ever listen to you?"
"It's a sad day when you're so keen to say you told me so you'll look to a demon to back you up," says the second boy, previously addressed as Rayne.
"The demon is prettier than you," the grumbly one points out, although the logic behind this statement is anybody's guess.
"The important thing," says Rayne, "is will you clean—" Ripper elbows him in the ribs. "What?"
"We just accidentally summoned an unknown kind of demon from an unknown universe," says Ripper, "the state of our floor is not our biggest problem anymore, will you give it a rest."
"So, tell me about this place. Like I'm from outer space, because I can tell you're speaking British English and can guess you're counting years from the supposed birth of Christ and you apparently play something I can identify as a guitar, but I'm not sure what depth of similarity that implies."
"I'm not," says Rayne. "What do you want to know about? Magic?"
"What do you know about magic," says Ripper.
"More than you do."
Ripper picks up the not-quite-useless demon summoning text and throws it at him, not very hard. It bounces off his arm.
"Ow."
"The basics of magic, and just for completeness can you - I don't know, list the continents and name random extremely famous people and things in case I don't recognize them all? If you're thorough I might even neaten the apartment some, although I draw the line at interacting with anything you may have puked on."
"We haven't puked on anything," says Ripper. "We're not that kind of drunk."
"I don't think the nice demon needs to know what kind of drunk we are, Ripper. Famous people and things..."
"Hey, is Australia a continent?"
"Probably."
"Ha, you missed one."
"See, you're not too drunk to explain it after all," says Rayne.
"I can make arbitrary nonmagical matter. If wanted to suck the entire planet into a black hole, it would already be done. My knowhow is not the limiting factor on how bad I can get, but it might be the limiting factor on how much useful stuff I can accomplish while I'm here."
"Arbitrary nonmagical matter includes, like, the ability to patch your ozone layer, I can't remember if that's known to be a problem yet? It's a problem later. My Earth, anyway. There's things I can't do, though, even with my sci-fi gadgets from the time travel part, so maybe magic could make me more well-rounded as an ozone-layer-patcher-errant."
Cam can't heal the table as seamlessly as an angel could, but with a firmly attached layer of intervening wood knitting the broken parts together he can do a passable job. It looks pretty much like a crappy apartment in the First World just before the turn of the millennium ought to look. Except for the booklist, maybe.
"Oh, what's the worst that could happen?" chirps Rayne. Ripper gives him a dirty look.
Cam gives up on talking to them. He does as much cleaning as he feels like and then makes an upholstery cover on their couch because he doesn't quite trust it and flops thereupon and makes himself rashers of bacon to nibble on, one at a time, and a stick-shaped computer with a futuristic screen projection to operate with the other hand.
He goes into the kitchen. Rayne is sitting in a chair beside a long-since-boiled electric kettle and two mugs containing one dry teabag each. He is indeed asleep. Ripper sighs and picks up the kettle to refill it with fresh water.
"Sory, where was I?"
"I'm outlining my plans so you can decide if you want to come along for the ride," Cam clarifies. "Arizona, check for mini-me, build house in the desert, loiter in a library and hope nobody asks why my coat's so lumpy, go home and make my own copies of useful references, sometime in between these errands I can hop you back to I'm assuming somewhere in Britain."
He slows down when they approach Phoenix.
He lands in the desert a ways away from the city but within reasonable walking distance of the highway, and makes a large rock between the road and his ship to conceal it from casual view, and hops out.
They come to a house.
"That," sighs Cam, "is not my mom's house. If there is a tiny me he is probably not gonna be easy to find."
Then Cam opens the front door. There is furniture and plumbing and two bedrooms and a prettily-carpeted living area, but he has neglected to include a kitchen, probably because he can just make food out of nothing.
There is a bookshelf. Cam picks up a volume of the encyclopedia on it and starts flipping through it.
"One thing I find really interesting about my magic, actually, is that it becomes so much more useful as more things about physics and engineering get learned. Hell is naturally an infinite empty void. Most demons live on a giant plane of solid gold that someone grew until it was big enough to exert a gee. It's extremely tacky. No one had discovered black holes or, like, gravity, at the time."
"In human culture, yes, absolutely. Demons pop into existence fully formed and adult, and when they aren't ex-humans, they don't even come with languages installed. Talking to each other at all took a while and might still be unpopular if it weren't for the fact that we tend to appear near other demons. Writing took a while, the scientific method took a while, and there's not much, like - improving the welfare of demonkind, motivation. We are indestructible and can all have whatever we want any time."
"The angels have a different result from a loosely similar background situation, admittedly - but they aren't quite as powerful, even if you give them a head start by supplying all the cloudy fluff Heaven is made of that they can use. Fairyland is way more interesting all by itself than a void or an expanse of fluff, but they don't have much good magic helping them along with the sciencing, they're pretty much just telekinetics."
"I'm going to have to take your word for it." Page page page. "Okay, this world is missing a couple key notable figures who I would have expected to appear in the encyclopedia and know for a fact were only notable because of things related to summonings they did. So either the magic's too different, those people outright don't exist, or it's not straightforward to go from being able to summon to being rich and famous."
"...Depends what kind of magic people," he says. "Heavily depends. Set you on fire, drain all the life out of you, imprison you in a statue for a thousand years, turn you into a rat, lock you in a hell dimension, curse you, get another demon to possess you... I mean, most magic people can't do most of those things, but some magic people can do some of them."
"Can you expand on that? Is the fire and/or statue in fact literally magical or can I solve those problems with water or aqua regia or whatever? What are hell dimensions like, what are curses like, how does possession work, and what precisely is life such that it can be drained out of one?"
"Fire can be magical or not, statue's almost certainly going to be magical - covering you in a layer of stone would be harder than turning you into stone or trapping your soul in a statue somewhere. Hell dimensions are all different from each other but they're usually not nice, usually full of demons, and often have a lot of fire. Curses vary, I could list twenty more things without covering half of it, and I don't have the right books on hand to make sure of the details anyway. Possession also varies, but the basic idea is that you're sharing your body with something other than you and it's more in control than you are. And there's always going to be things I can't tell you about because I've never heard of them."
Ripper starts scribbling. He crosses out enough mistakes that he has to turn the paper over and start fresh, but what he ends up with is a very neat list of a lot of books - very few of which seem to have authors - with the occasional brief note along the lines of 'sensitive to Latin' or 'corrupting influence unless opened and read with ritual'.
"They don't have authors. I can probably guess date of publication for some of those if that will help, at least as close as which half of which century. I think the closest you'll get to an innocuous magical effect is the ones that do strange things if you speak Latin around them."
"All the people I know who know anything about magic know less about magic than I do," he says. "And the people I used to know who know more about magic than I do would be a bad idea for you to go talking to even if you hid the wings and tail. They'd find out somehow. It wouldn't go well. They're not that keen on outsiders regardless."
"Some kind of magic detector, or someone scrying to see where you came from, or if you said something weird and they realized you weren't from this world... and, again, even if you didn't trip anything up that way, they still wouldn't just tell you things about magic if you showed up out of nowhere asking."
"Yeah. They could be shady types and suggest, I don't know, the Gem of Amara. Don't make any Gems of Amara. It's supposedly a jewel that confers absolute immortality on any vampire who wears it. Completely useless to you, it'd make some scheming bastard rich, and then there'd be fifteen unkillable vampires in the world."
"Okay. Getting rid of me's not hard. You just focus on wanting to for about a minute. Nothing arduous or costly that it's extra inconvenient to have both of you need to try. And here is a circle you can use to get a random fairy, who you dismiss the same way. Optionally after having a brief chat with them, but please don't try getting them to clean your apartment. Or do anything else. Just summon and dismiss." Cam makes a sheet of paper with an appropriate circle drawn on it.
And eventually Cam goes and patches the ozone with Ripper in tow, and then drops Ripper off at home with a kiss goodbye and that fairy summoning circle and half a walkie-talkie pair that should work while Cam's half is most places on Earth if need be, and he flies away again.