It's set sometime in the future. I think Xander basically rules the world, and his hyena has something to do with it. He also has a son (or teenage clone, I can't remember).
The part I can remember clearly is Xander's son trying to get into Spike's pants, but Spike turns him down cause he wants the real Xander. Instead he takes it upon himself to protect the boy.
There was also something in there about Xander's hyena needing to mate, and only wanting to it to be Spike (I think). The boys get together in the end I know for sure.
Any help would be much appreciated. Thank in advance. :)
Edit: it was Slip Slide Melting