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—
The video feed starts, and the employee turns out to be a fairly sharp-looking woman in her thirties.
"Yeah, I made sure to get someone good, cutting costs here would do us no favours."
Thorn's wings stop beating, for a moment, and then start long enough for him to turn to face his entourage and sign; one of them looks away in time and streaks ahead of the group, but the rest collapse to the ground, Thorn among them. Promise dives for the microphone and un-stops Verve and sends her after the fleeing fairy to heal her ears.
And Mortal's employee will sign WHISPER YOUR NAME TO YELLOW at the appropriate time.
And Promise and Mortal will, of course, hear it too.
Promise shivers when he whispers "Syracerix". "That's it," she confirms. "Get the fleeing fairy's name so Verve can stop her, she's getting away -"
"They're probably all deaf. Yellow, order him to give you the fleeing fairy's name, then tell him he may breathe and allow his vassals to breathe."
Promise is hyperventilating.
Mortal notices this. "Yellow, order him to, taking no extraneous actions, do exactly and only what he needs to do to get his own ears healed." Releasing the button, he turns to Promise. "Are you alright? Do you need—I don't know, do you prefer not to watch or something?"
Thorn orders one of his sorcerers to heal his ears. He does.
He nods, and reroutes his microphone to order Thorn himself. "Answer all our questions completely and truthfully, giving priority to information that in your sincere best up-to-date model of us we would find most relevant. Obey the spirit of every order as intended by its giver when its phrasing is ambiguous, again according to your sincere best up-to-date model of the order giver. Inform us of any loopholes you detect in any orders we give or have given you and do not exploit them."
"Amend that," Promise says sharply, "to mean that you are to obey the composer-intended spirit of orders enforced upon you, and directives conveyed as subcomponents of orders enforced upon you, where that enforcement is by myself, the person you just heard speaking, or anyone you sincerely according to your best up to date model of the world expect to be an agent for one of the two of us."
And now Thorn is silent.
"What are you hoping we won't ask you about?" he voices in lieu of commenting on Promise's hotness.
"What my vassals will do in response to my delayed arrival," Thorn says, "what I am hoping you will not do with me, Blossom's name, where your mother is."
"Please answer those questions as if I had asked them." The 'please' is merely Sadde's Britishness showing, the order's quite enforced.
"As the news percolates the unimportant will scatter and the important will piece together directions to a backup court site and develop plans to retrieve me. I hope you will not ignore Promise's likely advice in favor of more elaborate revenge. Arilahera." (Promise nods.) "In the court on the river, in the sub-basement."
"I," he tries to inject as much venom into that as he can, "would not be so stupid or small-minded as to seek revenge. Even if you had nothing I wanted I would still at worst turn you into a sparrow."
"What steps would you take in my position to prevent your successful rescue at the hands of your subordinates?"