Buffy the Vampire Slayer: Out of the Madhouse (The Gatekeeper Trilogy, #1)

Sunnydale is being besieged by dark forces. But even with Buffy providing her unique style of damage control, it's more than one Slayer can handle - especially since the abominations are coming from a centuries-old portal through time and space.
https://openlibrary.org/works/OL14963...