The blood of Carthage - Christopher Golden

The gang is off to college and Buffy's whole world is changing. How much education does a girl who's destined to kill monsters her whole life really need? To quell her confusion, Buffy throws herself into Slaying with wild abandon and disastrous results. Her killing of Sunnydale's answer to big foot may just bring about the rising of the demon Ky-Laag, and the end of the world. And the only group who know what's going on and who want to stop it, the mysterious Blood of Carthage, also want to kill Buffy for starting it all.