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—
"I rescind all your orders."
(Because if Promise was captured, this is an emergency, and she'd thank her for it. Probably.)
And she hangs up, gets up from her chair, goes to the unremarkable spot where her gate is, goes to fairyland, walks a bit towards where the gate that leads to London is, and is in the alley again.
There's Promise. "My new tree's still a little cramped but it will fit all three of us and some stuff."
She nods, trying not to let it show. "I should probably show you our safe houses so you can gate there?"
So she ducks back to fairyland through the original gate, and starts leading the way to the gate to HQ.
is apparently empty.
It's a small room, with a door over there across it. But instead of making for the door, Mortal makes for an arbitrary location on a wall. There, she presses her hand on an arbitrary spot, revealing a little compartment containing a black plastic box with a couple of buttons, two little lights (one green and one red, the red currently on), and a glass screen. She presses her right index, middle, and ring fingers against the screen, and it beeps, turning the green light on and the red one off.
"Later we should register your fingerprints here so you can disable the security system yourself."
"If anyone spends more than fifteen seconds in this room or tries to open that door without disabling the system first, they are shot full of bullets. I can also deactivate it with my voice, but I wanted to demonstrate the other way to you because apparently fairy voices make sound analysing software go crazy so you'll need that if you ever come here without me."
"Of course. Is this enough for you to gate here, or should I give you a tour?"
"Should I gate into this room in particular? If so this is enough."
"Yeah, 'cause of the traps. The other four places have similar rooms, though."
This level has windows, which reveal a woods surrounding the place, and they all have reinforced metal shutters, not to mention being bulletproof, Mortal explains. This has all made quite a dent on her savings, but that's not a problem at the time.
"Money is pretty impressive," she agrees, "but my mother and I cheated. Very different things are scarce here than in fairyland, with sorcery around."
"The Earth is finite, and raw material goods come in limited supply. People value things like gold or diamonds or precious stones and transmuting them with sorcery is fairly easy."