curse of strahd (Dark, has a great BBEG, and has a goal even if the PCs don't know it at first)Take three big adventure books and mash them together for a new campaign.
Strixhaven (connections matter, and mixed with the needing alies of the above works really well)
Sunless Citedel (It's low level, it has a town and a dungeon, and you can make enemies into allies)
scrub off all the serial numbers...
there is a dark lord (I'm making mine a Ghoul Queen instead of a vampire) she rules over a small bit of land (I'm going with valley... I don't know how I would force PCs to stay maybe do the mists of ravenloft but maybe just do 'its the game') and within in she rules allufly. There are a handful of towns each run by there own lord mayor or counsel... only 1 is safe at all with awall self contained with something living in the old abby (Instead of a corrupted deva I am going to do redeemed demon... he is chaoric good and trying but he has to stay mostly hidden). none of the cities has a large force, just some few guards... but they all work with the red tower.
The red tower is an academy to control magic... people who have smarts and want training, people born with magic, and even people who cut bad deals and have magic all go there eventually to learn to control there magic... PCs start at or near the tower...
the ghoul queen doesn't rule from a castle on high... but deep in the ground, a sunken city... years ago an earthquake sent a village into the underdark, it is now the seat of the ghoul queen and her consort the lord of the goblins... but the goblin lord is at war with the kobolds that are in the caves nearby... and those kobolds have there own queen a half dragon kobold sorceress and her 'half brother' a wyrmling white dragon.
ghoul queen is a lesser agent of Orcus.... and as such the end goal is to overthrow her, but you need the divination teacher at the tower to look into your fate and read where the alies and weapons you will need are... oh and the Ghoul queen LOVES messing with people... and sometimes taking in people for dinner (and she doesn't even always eat them)
the final exam of this game isn't pass or fail... it's do or die.