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—
"...oh. Right." Slight disappointment? Surely not. "Can I try it on you, then?"
"The other two might still work. I think mortal language might be more consistently legible in stamped or assembled form."
"Yeah. I don't have a stamp on me, but—" He grabs a phone, dials a number. "I want stamps, those kinds you can change letters around, and ink. Yes. Yeah. No, no—yes. I also want five stamps saying stop, yell, your, name, say—yes, five of each. One second—" He looks at Promise. "Any other good words?"
"Order, them, to, don't, no, not, do—make it ten of each, yes, and twenty of the kind that you can change. Yes, as soon as possible. Thank you." He puts down his phone. "We'll get stamps in about an hour."
"Yep. I mean, the final utopic plan is moving humanity to a post-scarce society and fairyland to a post-vassalisation society and I'm not above cheating my way there."
"Yup. Anyway, let's see, any other obvious ways to fiddle with writing or signs or transmitting orders visually?"
"So what exactly counts as code? Like, say, what if I invented code that meant a dash is a certain word or something? What would it take for it to... work?"
"...I can't decide that a sound 'means stop' or some longer sentence. You probably can't either but it's maybe worth a try."
"I mean, something decides that a sound humans use means stop. There are languages with only a handful of speakers alive on Earth, there are languages with no native speakers, whose real pronunciation isn't even certain, and I'm wondering where the boundary is."
"Making something up and agreeing on it with your employee is worth testing."
"My thoughts exactly." He opens an image editor and draws a slash, then starts composing an email to his employee with it attached.
He sends a couple more images with meanings such as 'order' and 'them' and 'to' (even though that's quite anglocentric), and then a little star thing is supposed to mean "unfold your wings." After a little bit of back-and-forth, he turns back to Promise. "Let's see if this was enough to take?"