The world has moved from having 2000 "potentials" to 2000 full-blown Slayers. And not all of those are good. What do you do with them? Giles discovers one who has turned bad, and calls in Faith for help. Episodes #6-9 tell the story of Faith and the rogue Slayer. Then in Episode #10 we learn why Willow is keeping Buffy and Kennedy apart.
This continues to be a great "8th season" of Buffy, with the smart mouth dialogue, dark corners of the mind, and a fair bit of action. The writers have a strange view of England, though.