Crossover with Anita Blake
At the end of Dopplegangland while doing the spell to send Vamp Willow back to her reality, the human Willow is accidentally sent to AB-verse and vamped. I don't mind the "how" - she could be vamped by the spell, or you could have a vamp in the AB-verse turn her.
Jean-Claude and company have to deal with her.
Maybe the Scoobies attempt some kind of rescue?
I would prefer the focus to be on AB characters other than Anita, but I won't insist on it. You writers are always surprising me and making me like things I didn't think I ...