Spike’s not too sure why he’s headed back to Sunnydale, but in his alcohol-addled mind, he knows it’s where he has to go to prove to Dru that he hasn’t gone soft. He’d made the deal with the Slayer for Dru’s sake alone (why can’t the crazy bitch understand that?), and now that he doesn’t need her anymore –
The picture in his head of just what he’ll do now that he doesn’t need the Slayer anymore is a bit muzzy, but Spike’s sure it will come to him. Something appropriately evil and despicable and not soft.
His first stop (post smashing of the Welcome to Sunnydale! sign) is the factory. He can’t quite find whatever it is he’s looking for there, only the burnt remains of Dru’s dollies, so it’s on to the mansion. It’s cold and dark and lifeless, which, come to think of it, it’s always been, what with them being undead and all. But it’s also empty. When he manages to force himself to think it through, it makes a certain sense. World didn’t get sucked into hell, ergo the Slayer must’ve defeated Angelus. Ergo empty mansion.
Spike’s next stop is the Slayer’s house. It turns out to be empty and lifeless as well. He squints at it a while, then passes out, still squinting.
He wakes up on fire.
After rolling the blacked-out window back up and dousing himself, he tries to figure out what to do next. His brain, still pleasantly marinated, proves uncooperative. Something about the Slayer... the Slayer...
Right. Find her and kill her. Wear her guts for garters, bring Dru her head, etc.
Except the Slayer’s not home. Spike ponders, trying to piece together the clues. Daylight. Empty house. Teenage Slayer...
He takes a celebratory drink when he figures it out, and heads for the school.