Practical Magic is an adventure full of personality. Many personalities in fact.
A necromancer whose work is focused on making skilled undead even better at their jobs, he sees corpses that aren't being put to productive purposes as wasted material. He gets wind of another spellcaster with a sense for putting magic and inventions to practical uses and sees an opportunity for the two of them to work together, bettering both their efforts.
He sends an invitation to meet, but the message doesn't arrive because her boyfriend is breaking up with her. So the necromancer has his very smart undead servant kidnap the wizard.
The boyfriend is a dominated servant of a mermaid vampire. So is his cousin.
The mermaid vampire has the boyfriend lure the downtrodden, poor, or depressed to her lair under the guise that she is a fortune teller that can help relieve them of their burdens. She then convinces the victims to go out of the world in an exotic way . . . as her food.
The boyfriend's cousin has turned evil and now wants to become a vampire.
The ghast that kidnapped the wizard is addicted to fine clothes and fancy furnishings. He owns a Hat of Disguise that lets him pose as himself before being turned into a ghast, and allowed him to pull off the kidnapping.
The kidnapped wizard has heard out the necromancer's idea and come around to giving it serious consideration. She however has her own plan for how things should work.
Much of the adventure takes place in the two hidden lairs and will require time spent in the water.
Now we just need to figure out where everything is and who else might be involved.
According to the module the mermaid vampire's lair is about 300' off the coast in about 20' of water, with a bunch of sharks around it. This could be almost anywhere as long as it stays not too far from Ptolus. Victims need to be able to reach the lair and her agents need to be able to return to the city fairly quickly, but it all needs to remain unnoticed. At first I thought to put it south of Beacon Island, but reading further into the adventure made it more likely that the necromancer's lair is under the south end of the island. Two major lairs that close together doesn't work for me.
Then I looked north of the docks. It might work, but it starts to come close to the territory of the Covenant of Blood and their Sahuagin allies. it could certainly work. She might be one of the 6 vampires in the Covenant. She's good with sharks and so are the Sahuagin. The drawback is that PCs that defeat or drive her away make enemies of the Covenant, the Sahuagin, the Balacazars, and all of their other allies. That's a lot of weight bearing down on the player characters. Maybe the mermaid vampire is viewed as unwanted competition by the Covenant and they'd like to see her gone, one way or another.
"One thing about living in Ptolus I never could stomach is all the damned vampires."
Studying necromancy is not technically illegal in Ptolus, but creating undead or bringing undead into the city is outlawed. This is reason for the necromancer to have a hidden lair off shore. The lair is fairly large so he needs a big place to put it and under the south end of Beacon Island seems perfect. The island already has a reputation of being haunted. The necromancer is a known entity, and has in the past aided in fighting off pirates, so while dealing with unsavory things, nobody has gone out of their way to try and put an end to his practice.
Interesting is a great way to describe this adventure. It is possible for characters to make enemies of just about everyone in the module if enemies aren't killed. They could also end up with some bizarre semi-allies depending on their own sense of morals.
