“ A man is taken in for a crime years ago. Any who ask or willing to listen, he tells a tale of how he ended up in such a position. So far fetched is the story that many believe it to be false. Perhaps the adventurer who came to town would like to listen to the man's tale?”
“ With a huge number of sacrificial victims, another realm long ago secretly bound a Prince of the land spirits, Iorstonn by name, thus ensuring the fertility, and improving the magical defences, of their realm. But binding that Prince to one spot has disrupted the weather and magical patterns (ley lines?) over half the continent. Things have become bad enough that a coalition has been formed to rectify the situation, once divinations have established the cause.
Your party is one of the teams assembled to do the rectification: find the binding object and steal it ('so that we can destroy it here in our realm, of course'...*) or destroy it over there. Presumably the Prince will be grateful to his rescuers and angry at the binders, but with a greater spirit like Iorstonn one can never be sure: such beings are 'tricksy'.
* Of course, the rulers of our realm might want to control Iorstonn for their own ends...”
“ In the harbour of a major city a large and terrifying ship made of human nails docks. Nobody seems to inhabit this ominous vessel, someone needs to go on board and unveil the mystery. In comes the PCs.”
