“ The PCs have travelled long and far. As nightfall approaches a mighty storm is unleashed. Luckily there is a lush wood nearby the path.
A good shelter for the rage of the unnamed weather gods it seams at first. As the PCs enter under the roof of this dense wood, they are welcomed by only a few drops wich is allowed trough the thick forest crown. A fire is offcourse required to warm the weary bones of the travellers. As one of the party is set to the task of collecting firewood the others settle down at a suitable location. But alas, they did not know the perils of this forest. But it seems clear to the rest of the party that something ill is at work as the woodcutters scream echo from afar.”
“ 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...”