I know this was an older fiction and I think Evenstar could have possibly been the author but I can't remember for sure. Spike just got his soul and is starting a relationship up with Buffy again. Sunnydale has been hit with a crazy amount of rain causing flooding and Giles figures out it is an apocalypse. I don't remember how but the Scoobies need the head of a Medusa like demon to stop it so I think Buffy and Spike actually go to Greece by teleportation thanks to Anya. While fighting the Medusa Spike gets turned to stone but Buffy manages to save him. He does get poisoned by the blood from the Medusa head and falls into a coma. The Scoobies and Buffy think he's dead but eventually he wakes up a human with Slayer abilities. Hope someone knows the title and where to find it because I've been racking my brain to no avail | 
