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—
"Just minimise, then," he agrees. "As for the plans... Remove the 'could,' say 'is' instead?"
"Sand's existence," says Promise, "is, obviously, related to your plans. The problem is 'related', not 'could'."
"Oh, right, hmm. Just the plan's existence, then? I don't want to just make a list of all the things the plan involves."
"Maybe something like 'minimize risk of discovery of me, this device, and irregular behavior you or Verve take at my direction'. And maybe 'our' not 'my' so they can't defect if another voice takes over."
He nods, and furrows his brows. "I've been using 'I' and 'my plan' to Verve throughout, I should probably revise her orders to include anyone whose voice she hears through the earbud."
Then, with both Mortal and Promise safely away from her, the stop order is rescinded.
They keep eyes and ears on her, with a half-second time lag, having her arrive there from the right direction, and when she does, they look around with infrared for any hidden fairies.
And in any case they should probably worry about the fairy who's going to question Verve about her trip before they start worrying about invisible surveillance fairies.
Mortal belays the order and hopes the ones he and Promise layered on Verve before are good enough to hold up to scrutiny.
Well, terrific, then. As soon as they deem it safe enough, they'll order her to put down her larger invisible packages in a corner, and try to aim for the best moment to get Sand alone.
Then one of them orders Sand as planned, while the other gets Verve to attach the extra, invisible cameras in addition to the earbuds.
And then, once again, they wait, keeping a remote eye on both vassals.
...yyyyeah it kinda is. But it'd also be exactly the part where any halfway smart surveillance fairy would want to catch them unawares so they surveil.
(Also. Awkward is. Not the only thing this part is.)