“ 'Look, lad! You see the streak of glowing green off the larboard bow? Them's the bright waters!'
While the lad peered intently at the eerie glow, the old salt continued. 'Entire ships have been lost to the Bright, lad, for once you let it surround you, you'll never touch land again!'”
“ Half hour off the Harrow Road you find it, Fool's Grave. Amid an overgrown garden sits a single tombstone. Carved neatly into the weathered slab is the word 'Fool,' with a symbol underneath matching the signet ring you found.”
“ 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...”