"Not 'probably'. I need to be able to recognize it. When would be the least suspicious time for me to collect it?"
"All right. When I've left this room, act normally except insofar as is necessary to plant the Silmaril, the described bundle around it sufficient to conceal it, and the key to its box without any suspicion you can possibly evade or defuse. As necessary to maintain the fiction but not extraneously or in any tellingly irregular manner, tell people I am taking food that you offered me. If anyone is suspicious enough to make trouble in the relevant time frame, telepath me their name and face and what's going on in as much detail as I would need to find them and address the situation informedly. Continue to minimize suspicion until I have been gone with the Silmaril for two hours. At that time you may freely act. Do you detect any flaws in this plan from my perspective?"
"The Silmaril will glow even with that much wrapping if you wait until it's dark. You should leave during the day. I think it'll still be day in two hours. I haven't been outside, I'm not sure. The House of Fëanor will try to kill you for stealing their Silmaril. I don't know if that's a flaw in the plan from your perspective."
Nod. Sigh. "I won't insult you by thanking you. Plan stands without revision. If you have to explain what we were talking about, pretend we were discussing something intensely private to me and also my need for food." She opens the door, looks shaken and grateful, and says, "- thank you for seeing me, Lady Elwing."
And Promise goes out and makes sure she knows where the yard is and makes herself innocuous for an hour and then goes to check the yard again.
Fly fly fly why is this so fucking heavy why didn't they mention it GLOWS fly fly fly.
Great. Then she can lug the damn thing all the way back to the fortress.
She goes and plunks it down. "You didn't tell me it glowed. You didn't tell me that it plus enough stuff to make it not visibly glow weighs half as much as I do!"
"I'm hungry. I'm otherwise fine. They sang me almost all healed, I didn't know there was mortal magic. Is something wrong with it? Did they have a decoy or something?"