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—
"There's other stuff that could get us even more money like oil, but that's harder to cover and anyway bringing more oil to Earth is a somewhat undesirable solution," she says, as she leads the way back upstairs. "System inactive," she says out loud before she opens the door to the empty room.
"Dead matter under incredible pressures in the Earth's crust over millions of years becomes an oil that can be used for manufacturing many things or as fuel. And what do you mean by functional?" she asks as she makes her way to the undistinguished spot where her gate is.
"Oh, it did a thing, I was deactivating the system while we're here." Into fairyland! Close the gate once Promise's through. "It reactivates whenever it has spent more than fifteen seconds detecting no activity."
Next location! Another ten minutes of walking, and then a room very similar to the one they arrived in, and Mortal says "System inactive" again once they walk in instead of doing the handprint thing.
Tour of the second place! It's very similar to the first but only has one floor. "We're in a different continent, here," she says, gesturing at the window to indicate the snow piling outside.
"No, that one would be Antarctica and there are basically no people there. It could be a good idea to make a base there except transporting anything would be impossible. Antarctica is at the extreme south, we're at the very north—do cardinal directions even exist in fairyland?"
Back to fairyland, close the gate after Promise, next place.
"...Directions? The part of Fairyland you've been is south of the Queenscourt."
"It's just that, on Earth, there's a north pole and a south pole, which are the points the Earth's axis of rotation intersects with its surface more or less, and the east and west directions which are defined with respect to those."
"Well, in Fairyland they're just directions, I think. ...If a sun is going to rise, it does it in the east?"
"It does that on Earth too but that's because there's only one Sun, which is a giant ball of plasma around which the Earth revolves, and the east is the direction from which it rises from the perspective of someone there."
"Apparently, yeah. Or perhaps this translation thing is just picking the direction in which suns rise and calling it east for me, that actually is probably what's going on here."
"It is interesting though that there is a single direction in which all suns rise in fairyland."
"I'm not actually positive about that; it's a little hard to compare while being certain you weren't turned around."
"Well, it's at least consistent enough that people presumably don't get lost when they think 'south of Queenscourt'?"