‘You are freed from all cares brothers and sisters! All worries! All need to toil and labour for the baron’s taxes, in the guild’s fields and for the peddler’s wares! All the drink you could ever need!’
Final words of an extremely drunk hedge conjurer by name of Oates Greenlock.
A goddess with a holy object of veneration in every pocket, wallet and bank; as well as down the sides of the big comfy chair in the inn.
"A demonic plant? Don't be daft, go research something useful to society."
"But-but the p-plant! It's evil! It must be destroyed!"
"Now the flowers bloom all year round thanks to the most holy Spirit of Urban flora. It just takes a little blood."
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...