This is post 12 out of 25 in the Cygnus Series of a September of Short Adventures.
(This one works best if there's a half-elf in the party.)
Long elevator pitch: There is an evil high-level magic-user, Brunhoff of Kent, who has fallen insanely in love with Lolth, the demon queen of the Drow. He yearns to call her to him with the most powerful cacodemon spell he can muster. He gets it in his head that to do this, he requires not only the blood of a human victim for the material component of this spell, but a perfect blend of human, elf, and dwarf blood.
Brunhoff employed dozens of sages to (magically) trace the genealogies of everyone within a hundred miles. He discovered that one of the human PCs had two very interesting great-great-great-grand-ancestors: one was an elf, and one was a dwarf! (*) If there is a half-elf PC, then only one remote ancestor is needed. In any case, in this person the three types of blood are "co-mingled" perfectly!
Why does he believe this will do any good? Brunhoff learned that Lolth has expanded her dominion in the Abyss. She has totally conquered the Pharisee Elves of Caer Sidi, as well as the Mountain Dwarfs of Maldev. (You know your Q1 well, right? Both are other worlds in the prime material plane connected to Lolth's extradimensional web...) Brunhoff believes that this blood will demonstrate to Lolth that he, too, has conquered both elves and dwarfs, as well as those pesky humans who are always attacking her other allies, and thus gain her special favor.
So how might this play out?
One day, while walking down the street in a town or village, a local person, commonly dressed but carrying a high-quality fencing sword, bumps into the PC with the special blood. "Why don't you watch where you're going, X?" (Please insert for X any clearly demeaning epithet that emphasizes something negative about the PC's appearance or parentage.) No matter how the PC reacts, there's a loud challenge to a duel, right here on the spot. A crowd gathers.
Brunhoff is there, too, dressed as a mild-mannered cleric pushing a wheelbarrow of turnips for his monastery. He expects his hired hand (a high-level fighter) to defeat the PC in a duel. Then he will offer to take the injured/dying PC back to the monastery to be healed. Even if he can't kill the PC, he hopes to extract as much blood as he needs at leisure.
If the PCs run away, or if the PC wins the duel, then Brunhoff will go with a Plan B. The "cleric" will make himself an innocent-seeming pest to the PCs and follow them around a bit, maybe asking for their help with some local roughnecks who are threatening the safety of his (fake!) monastery. If all else fails, he may resort to some charm or geas action when the PC isn't surrounded by his or her friends.
What will happen next? That's about all I've got on this one, unfortunately. If you like the idea, I'm curious to know where you'd take it.
(*) The story of the dwarven female who, long ago, wanted to leave the mines and explore the world is a fascinating one that shouldn't be forgotten. She fell in love with a local lad, and luckily found a magical friend who helped her polymorph herself into a gorgeous human woman, and the rest is history....