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—
"So, basically, wait 'til he's genuinely alone?" Pause. She presses Verve's button and says, "As soon as you believe you can do that without anyone noticing it or finding it strange, bob your head a little bit twice if Thorn ever goes into his room alone, thrice if only rarely or almost never, and shake it a little bit once if never."
"I don't know," she sighs. "The mortal world has 'therapists' which are people whose job is helping other people deal with trauma and stuff, after this is done I could maybe hire one for you... Or, I dunno, talk, or maybe I could get you chocolate. I mean, I suppose talk isn't very feasible while we have to keep our eyes glued to the screen, but..."
"Well, they mostly talk to you about stuff and see how you're doing and help you develop healthy ways of dealing with trauma or some mental illnesses like depression—I'm not sure if plain speak translates the nuances of that word. As for chocolate, it's a type of food made from a seed that—how much do you know about mortal biology?"
"As opposed to bottling it up or having post-traumatic stress disorder or something. Which I don't think you'll do, but, like, sometimes it helps to just talk about the thing and stuff, to make it feel less bad. They spend, like, years studying this kind of thing, how people's psyches are affected by different things and how they deal and how to guide people towards good ways of not letting trauma affect their lives more than they want to."
"Well, I'm not a therapist, I don't know exactly what they do, but as far as I can tell fairy psychology isn't on the whole different than mortal psychology, so I don't expect therapy not to work."
"It's not in public, it's only with the one therapist, and they are legally prohibited from sharing any information about the patient with anyone else. They also take an oath to that effect. But anyway, yeah, I'm not gonna push it, just, you know, a thing I wanted you to be aware of if you wanted it."
"The quantity of supervising strangers isn't the meaningful difference between public and private."
"Fair enough," she nods. "Anyway, er, about chocolate, basically it makes mortals produce certain chemicals in our bodies that tend to help with feeling bad. Erm, it's a lot more complicated than that, and I'm pretty sure fairy biology works differently enough that it might not change anything."
"Well, it's... Not wholly a plant. It's made by mixing a seed and, usually, sugar, but often also milk. Shouldn't be hard to find chocolate without any milk in it, though."
"I imagine I could swallow it. It certainly wouldn't kill me. It might make me sick, I don't know, but it just seems really gross."
"Huh. ...I wonder if after this is done I'll be able to find amongst Thorn's ex-vassals someone who'd want to help me run experiments."