Just as well I slept on it. The Keys of Heraka-at looks like it went from “single adventure” to “opening of a two-campaign bundle”. I don’t have all the details yet, I’m feeling for the shape of it, but here’s what I’ve got so far.
It will be building on and making some minor changes to GreyKnight’s suggestion from a few days ago.
“The island is named Stormhame. The ancient line of the Thunder Kings once harnessed the potent magical energies of the skies in this place, and kept the surrounding areas under their rule. Although Stormhame’s influence has waned since the end of the Thunder Kings’ line, they are still a big player: they are active in the political arena, and the island also remains the home of the Shrine of Ferocity and its priests.”
I’m going to make a small change to an assumption most people might make from that description: the Donnerkonig (‘Thunder Kings’ in German is evidently ‘Donner Könige’, so this is a reasonable anglicization) not necessarily of the same family. They found it a useful fiction, and they were in the best position to see that their offspring were able to inherit their power, but ultimately it was truly a meritocracy, based on ability and worthiness.
And at the end, the Donnerkonig were not worthy.
The Donnerkonig originally came to power as several ‘small kings’ joined together, both magically and politically, to bring the kingdoms of the Sturmhame together into one. As with any good partnership, each gained — power and responsibility, freedom and duty, entitlement and obligation. For many generations this was sufficient, and the new status quo was maintained well. The power of the Donnerkonig was unchallenged in the region, and the heirs of the Donnerkonig well-chosen and well-trained to pick up the mantle.
After several centuries the inevitable decline began, culminating when one of the Donnerkonig reached to take more than was his share, trying to become the Donnerkonig rather than the leader of the Donnerkonig. In the end this led to the dissolution of Sturmhame into its component parts, the end of “the Donnerkonig line”, and Sturmhame being relegated to being once again a relatively minor power in the region. They are still active in the political arena, and legends speak of the return of the Donnerkonig.
The Keys of Heraka-at is a gateway adventure into a campaign that can lead to the potential return of the Donnerkonig, where the PCs learn the true history of the fall of the Donnerkonig line and can start the journey to potential rulership and reconstruction of Sturmhame.