The plan is refined and strengthened, contingencies are set to deal with various ways Thorn could've strengthened his defences, Mortal receives a very interesting email concerning one of their mother's contingency plans—namely that her assets have all been either frozen or transferred to Mortal themself, so Thorn doesn't have access to them -, and when Mortal and Promise judge there's nothing more to be gained from further planning they (eat dinner, sleep again, have breakfast, go over the plan once more when it's not completely fresh in their minds so they see if they come up with anything new, purchase Promise a mobile phone and a power generator to charge its battery in fairyland, eat lunch while Mortal teaches Promise how to use that, and) part ways.
On this side of the veil, Mortal gets to work. The first step: getting at least two safe houses, one for their HQ and the other for contact with the place near Thorn's court. They end up getting five, for redundancy's sake. The main HQ is near Seattle, the other four safe houses are in Greece, Russia, Japan, and Argentina. That, and getting the necessary existing equipment, is the easy part—you end up with contacts of the relevant sort when the bulk of your wealth comes from the kind of thing you can get with sorcery. The hard part is getting the various specific bits of technology that don't exist yet, including the the many types of trap and ammunition they'll need. Processing fairy voices with software turns out to be a dead end—apparently they're weird magical superpositions of sounds that make software go ?!?!?!?!?—but everything else, as agreed upon, can be made to spec nicely enough.
It'll take a couple of weeks beyond the one month for everything to be ready. Mortal hires someone who talks very fast.
And after the ball's going, there's not actually much for them to do with their time. They fret about details of the plan, order more redundant pieces of stuff (especially the to-spec stuff, not being mass-produced means they'd better have a lot of it to start with in case anything goes wrong), and have various antsy and anxious and calm and relaxed and terrified and panicked moods. A month is a long time...
At one point it occurs to Mortal that Promise might've decided to run away and not help, and then they'd never see her again and that would be terrible, and why would it be terrible anyway? It's just some fairy, fairies are evil, one must remember that. Even though she wasn't, of course, she was smart and resourceful and moral and ridiculously hot, and if they never see her again she'll never order them again and the tingly feelings won't ever happen again. Except what the heck, what are they even thinking? The answer, of course, is that they want to see Promise again. Why? To save their mother, of course. The only reason being ordered like that felt good was because Science. Of course. Of course.
The month passes—
"Hmm... I'm thinking that I could also make gates and at any one time at least one of us would stay here, but honestly it's not that big an inconvenience to have gates outside."
"Yeah. Although I'd have to leave a real door for you to use if you want to get into the tree when I'm not home."
"I assume this real door would also have the same keeping-people-out properties that just opening the tree trunk does?"
"Yeah, it just makes it more obvious from the outside that the tree is inhabited."
"Is there a way to make the tree open up instead when I in particular show up, or maybe create a more hidden kind of entrance? Also, just how far are we from—everything?"
"I can make the door unobtrusive, but not invisible or contingent. And it's a long inconvenient flight with a winter area and a mountain range between here and Thorn."
"Some individuals, a few small clusters, about six hours' flight southeast there's a glowgold colony, nobody big or liable to have capture on their minds first thing upon meeting an arbitrary fairy - you're another matter, but you would be no matter what."
"Alright. We still have a couple of things to do, then. There are a few tests I want to run, like seeing how well wards hold up against bullets, and I need to register your fingerprints in my security system so you can disable it without being shot. And it will take another couple of weeks for everything to be ready on my side of the veil."
"Okay. What should I ward? Are you sure fairies have the right kind of fingerprints?"
"I don't need a kind, per see, as long as your hand has a pattern that isn't likely to change and isn't some weird magical superposition of possible fingerprints it should be fine. As for what to ward, you probably have a better idea about what an appropriate target would be than I do."
"I don't think my fingerprints are magical. I'll go find a rock or something."
"And I'll go find a few guns. And actually, it occurs to me that a rock may not be the best subject because it's liable to blow into pieces if hit by a bullet, something that could absorb the impact better like a fairy body would would be better."
"I do not have any fairy bodies I want you to shoot at handy. I could get you a piece of wood."
"Oh, no, I meant, absorb the impact like a fairy body would, not, like—I wasn't suggesting you get a fairy body for me to test this. Yes, wood works."
Promise knits some branches together and detaches them from the tree. They fall to the ground with a thunk.
"Okay, starting with a simple handgun, if this is enough I shouldn't worry about wards in general, I think."
"Block is warded up to the best of my ability. Casting on my own tree gives me some homefield advantage that may shrink the gap between me and better sorcerers."
"Is it gonna do anything other than make the bullet bounce off? We might want to not be too close to it, too, if it bounces off in our direction. Oh, also, it's pretty loud," she says, reaching into the bag for earmuffs.
"...I could make it inaudible if I had a bit to look at it. And it'd slow down first, then bounce off, if the ward holds."
"Oh, inaudible's pretty good, yeah. Er, the loud part is the explosion that happens inside the gun, but it's the bullet that explodes, I'm not sure which of them you'd need to look at?" She hands Promise a handgun separated from the cartridge.