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—
"Mum! It's—it's me. You're—" He was about to say 'okay' but... "You're safe now. A friend and I—" Friend? Is Promise a friend? "We rescued you. We used a lot of those things you and I talked about. And we did it! We got Thorn, we stopped him, he'll never hurt you again, his name is Syracerix, he can't hurt you anymore now."
"I—it's your son. It's Sam—Sadde. It's Sadde." He hasn't really used his real name a lot in many years.
"We're—we're gonna get you out of there, we're gonna get you home, you'll be fine."
"I can get the gate set up as soon as Thorn has the earbud again."
And Promise gives Thorn instructions and he gives the nearest gate-capable sorcerer the earbud and she gives them a description of where they are and presently a gate is settling and someone is regularly trying to toss a rock through it.
Mortal watches it all with a kind of mesmerised fascination, as if it was terribly and unutterably interesting, except he looks like he has indigestion. He hasn't eaten since he woke up, though, so that's probably not it.
"Huh?" His eyes unglue from the screen and he turns to Promise. "Oh. Right. Yes. Feeling like eating anything in particular?" He looks at Yellow over there being boring. "Or you?"
"Whatever," Promise says.
"I'll go fetch that, then." He prepares something for himself, then brings blueberries and kale and a couple of bananas and cherry tomatoes and an apple to the fairies.
"This could take a while, maybe Thorn could go disable the rest of his courts and when the gate settles we'll know...?"
"I can set that up but it will mean we don't have bugs on the scene while we wait. Is that okay?"
"...watching it isn't doing my mental health any favours, getting this over and done with is, the vassals are not likely to do anything we don't want them to now."
So Promise issues orders - including a couple by proxy to Laura, just to be really sure, but those are gentle - and sends Thorn on his way.
And Mortal releases a breath he hadn't realised he'd been holding when he's no longer looking at his mother. "With this we should probably be done in less than two days, huh."