“ The characters are wandering through the bustling crowds of Lasopolis. A street conjuror is performing a simple summoning spell, something for the kiddies. A bit of odious purple powder in the fire, an incantation and out pops a saak-lizard or a muhmentarsh, writhing from the flaming brazier. But the conjuror has only a poor grasp of the arcane magical tongue. A few stuttered syllables could lead to Other Things coming through the brazier and giving the crowd more entertainment than they had paid for...”
“ 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...”
“ A plague is spreading trough the lands, the plague is actually an old woman carrying a stick. She walks from farm to farm spreading the plague. Can the PCs stop her without getting infected.”