Now they just have to get their hands on one. Whereupon I reject the obvious, and my heroine also knows that none of the noble families about have one -- the virtues of stones in this land being reason enough for people to keep track of them.
To be sure, the hero also knows that none of the families are reliable enough that they could go for help, especially in their peculiar state. It's very hard to ask for the use of a magical gemstone to help your lord when you in fact have your lord right there, in chains.
And then, kersplat in the middle of the outline, without a drop of inspiration. All very well to inflict it on my characters for a scene. Plopping them into a quest for a mobile object where they don't even have a notion where it has ever been does inspire such a scene. But you can't wring two out of it, if only because the readers will fall asleep.
Since the "reverse what happens next" won't work -- I have no notion what happens next -- the next recourse is "have a man with a gun in his hand come through the door." Which means I need to work out what that is in this world. . . obviously not someone with a bloodstone. . . but the other worker of fell magic could show up with a gemstone to attack. . . . hmm. . . .if she has superior abilities to find magical gems, maybe she can give a hint thereafter. Or perhaps her trail is significant.