Politics are behind it.
The muse sits and plays with brighter, more sparkly ides, which she had more fun with.
So I poke and shift about it. The basic political issues in a monarchy are not many. Overthrowing the king, establishing the succession -- whether the selection of the heir or the consort, seceding from the kingdom, gaining influence with the king in general or specific, pressing one's own claims, getting power of one's foes. . . .
In the abstract, a bit vague. But then, there is the matter of the attack, which is nasty and vicious and -- which is more important -- general. A glorious firebird that targets and burns specific victims can work as an assassin, but a general attack needs something different.
Perhaps at taking out the king, to exploit the vacuum? No, if that were it, the attack would happen again and again, which is awkward for the actual hero, who can't be there. Perhaps a false flag operation. . . or. . . and then I remember the origin story I was playing about for them, where the original villain was acting out of blind spiteful revenge in the wake of an irrevocable loss. Revenge! A wonderful trick. And one that has the advantage of letting the villain of the piece smash and destroy almost at random, out of spite.
Now I just have to figure out how to stop him. . .