“ Wytchwolde-Under-Ash, once a great Thorpe, was razed to the ground by the ruthless, and truth told more than slightly deranged, Porcelain Princess and her henchmen, the Purifiers. When the flames had at last subsided, and a kaleidoscope of swirling, dull-gray ash choked the sky, nine hundred acres of old growth iron spruce, black larch and weeping birch, was burned to utter cinders, along with the entire coven of witches comprising the Sisterhood of the Silver Teat.
Now, centuries later, the forests are somewhat re-grown, and the town of Foolswater stands where Wytchwolde-Under-Ash once did. It is said that even to this day, one can still find ashes in the otherwise potable well-water of this village. Once a year during the Winter Solstice, the 'Ash-Wind' comes to Foolswater, a suffocating black cloud that passes quickly but leaves dead birds and animals in its wake, darkening the trees, and staining the sky with black snow. The inhabitants of the village know better than to be caught outside during the day-long Ash-Wind. Everyone is locked snugly inside, singing old hymns that curse and re-curse the burned witches who once called this place home.”
“ 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...”