The hyperborean realm of the Eternal Flame
Clarence was singing in harmony as his kind is wont to do. Their singing reinforced the "song of existance". It was a somewhat important job, even though only a handful were needed rather than the hundreds that did so. He and others near him noticed the pin prick discordence in the weave of melody that was the material realm. Those dark alien notes rose up. The Angel Mind touch the Divine and followed the new sub melody. Humans would call it a plan. Angels dove to the material realm and, of course, if any world was going to be causing problems, it had to be Earth. Oh well, at least Clarence would know his way around.
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...