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—
"Hrrm... We're going to lose contact with this court soon, but we still have the radar near it to detect who comes and goes."
"If they get near enough we can just pull it back into the mortal world, they'll have to go through the gate and then their sorcerous protections will be gone."
"It wouldn't be ideal but I'm not sure what they'd be able to do with the information, especially when they wouldn't necessarily even be able to actually return to fairyland to spread it."
"If they go missing as soon as they find it that narrows down where it can be."
"No, I mean, in general, I'm not sure that them knowing where the gate is changes much of anything, their sorcery doesn't work at all in the mortal realm and we have terrain advantage here with all the security systems I got installed. We could pile up unconscious fairy bodies."
"...I think we're talking about different things. What I expect to happen, if a fairy finds one of our gates and goes through it, is that the security system I have installed in the empty rooms will neutralise them because all their wards and invisibility and whatnot will go away as soon as they step through."
"If they find it they can yell through it without stepping completely through, or guard it so we can't go out that way."
"Well, none of the three gates open to here, but hmm I should deactivate microphone relay from those rooms..." He starts doing that on the computer. "But yeah guarding is a problem. But... in any case, an unlikely one, it's still an invisible spot in the middle of the air fifty miles away from the court."
"Anyway, is that the plan, then? Get Verve out, invisible her, have her trap him between courts?"
"Not before Thorn ensconces himself somewhere and stays there, and that place will probably be wherever my mother is so just destroying it won't work," he sighs. "Anyway. I'll defer to your expertise, get Verve now or see if the secret can hold up 'til tomorrow?" he asks, gesturing at the screen with (what's left of) the court's feed.
"...Now, I think. Or, not this very minute but as soon as nobody with her name is paying attention."
"How about 'as soon as you sincerely believe you can do this without being stopped or followed, leave the court and travel towards the spot where I left you, then wait there for further orders'?
"Lets her potentially make detours, doesn't oblige her to hide from and avoid anyone she meets on the way."
"Wouldn't the 'being stopped or followed' take care of anyone she meets on the way? 'Being stopped or followed by anyone at any point in your journey,' maybe? As for detours... 'travel with maximum haste under these constraints'?"
"No, you said she should leave when she believes she can do it without being stopped or followed; she could encounter someone mid-journey that way. And can't ever be in a state to reasonably expect that's out of the question. Haste doesn't guarantee directness."
"Alright, so, 'as soon as you sincerely believe you can do this without being stopped or followed, and taking the fastest route to your destination while avoiding being detected, leave the court and travel towards the spot where I left you, then wait there for further orders'?"
"Avoid being detected while otherwise prioritizing taking the fastest route to your destination," amends Promise.
Button-press: "As soon as you sincerely believe you can do this without being stopped or followed, and avoiding being detected while otherwise prioritising taking the fastest route to your destination, leave the court and travel towards the spot where I left you, then wait there for further orders."