The PC's have been meandering around differant continents, and they wind up at this town. The people of this town are very suppressed, and do not like strangers. It seems as though the strangers they have dealt with in the past are pretty dangerous.
There is however a thriving community in this town...centered around a magic users guild. I admit, a very rare thing indeed.
As the PC's begin to find out things about this town, they find out some of the following things:
If the party tries to find out what happens to those who get taken away, they will find they are taken to a dead volcano, with a large valley inside. This valley does not go through seasons, and the trees are fruit trees, which always bear fruit. There is a portal into this valley. The portal of mourning. It opens up every three months on the soltice dates. Can you guess what time of day? At sunrise. Written on the archway of the portal is the purpose of the portal, valley, and since it is old and worn, when the portal was dicovered thirty years ago there was a loss of translation of the portal of "The Morning."
There is an evening portal too. But that one is the entrance to an old abandoned dwarven kingdom. It opens up every night. Each night, undead skeletons emerge with two tasks. Gather fruit. Look for newcomers, and "welcome" them to shelter. Skeletons will try to capture anyone alive with nets.
Inevitably the PC's will want to go dungeoning and kill off hoards of skeletons, and free lots of supressed people. Insert your own dungeon in this part or use a prefab.
Eventually, they will meet the lich in the dungeon. He will ask several questions about why they killed the skeletons. Now the poor people will starve... and so on and so forth. It will be increasingly aware that the lich is a good lich. The lich became a lich to forever take care of the orchard.
It turns out there is another lich. The Good lich is in fear of the Bad one, who happens to live in the town... heading the MU guild. The guild is a structure in which the Lich collects power, items, spells...it is great if the party has an MU who joined the guild without knowing. The guild is structured like a membership thing. Access to libraries is based on level of membership. Level of membership changes based on donations of magic items, artifacts, spells and of course money.
The possibilities branch out from there... But the deal is to free the good lich from the wrath of the bad. They could...
Any option is bound to piss someone off. Good or bad lich, or the 40 or so MU's who have invested their life's savings into the guild. But think of all those magic items that must be in there.