So basically, my players made a deal with a entity to kill a bunch of devils that are scattered across a continent disguised as mortals and bring to said entity the little crystals those devils drop when they are killed and sent back to hell. The problem is that during one of these confrontations, the king of the region they are currently in personally intervened when the devil was about to escape and killed It with his own hands (this king is really really powerful btw).
The thing is, when the crystal dropped on the ground, my players simply didn’t pick it, they forgot to go there and take it, so the king picked it up, and took it with him. The question that has been weighting in my head is, what would he logically do with it? Keep in mind he is actually a good guy, so he wouldn’t want to use it for power, considering it come from a devil. The most logical conclusion would be to hide it, right? To prevent someone from using it for evil.
Take into consideration those crystals are indestructible, and the party can’t tell the king they are after those crystals because of a deal with a entity because for some reasons connected to the main story, that would be a serious crime and they would hurt very much their relationship with this king and be in trouble with the kingdom. They’ll probably try to steal it in secret, but where should they go? Where would the king put it? In some kind of royal vault? Far from his palace or close to it so he can keep an eye on it?