You guys know who barely ever interacted face to face during BtVS? Spike and Oz. But if they ever did they'd get along, Istg. Like, Spike went to all those punk concerts, he was there when blues turned to jazz turned to pop, they would 100% bond.
And who knows demons if not Spike who embraced his demon and his human? So imagine if the night Oz broke out of his cage in S4 and the night Spike returns to Sunnydale after failing to regain the gem of Amara coincide. Instead of bonding with Veruca, Oz finds understanding in Spike. Because Spike sees a
someone just like him. After all, Spike lost his family, his pack, too. Darla is dead, Angel was always cruel to him and now has a soul that makes him cruel in a different way, and Drusilla rejected him. And Spike takes Oz hunting through the graveyards, they slaughter demons, play fight (Spike wins, Oz' wolf recognizes him as his superior for his fighting skill and his status as master of the hellmouth), and overall have a great time. By sunrise they are chilling in the crypt Oz keeps his cage in and Spike covers Oz with a blanket or his coat when he turns back.
They hang out, they chat, Oz reveals he felt at peace with the wolf for the first time since he got bitten, they agree for Spike to stay in the crypt for the day and hang out again the next night.
Oz never sleeps with Veruca but learns to accept the wolf as part of him while his wolf accepts him too. Spike abandons his Slayer-Killer plans too because he has a friend now and gets his external validation through other means than making himself out as the big bad.
Spike still gets kidnapped, but this time it's not because he's lurking around, stalking Buffy (although he still does that on occasion), but because he and Oz go out and Veruca finds them, tries to rape Oz, and Spike defends him, giving Oz the chance to run away. So Spike is kidnapped along side Veruca by the initiative.
When Oz wakes up outside his crypt and without Spike he panics, tries to find his pack mate, only to get close to campus and lose the scent. That's when Buffy and the scoobies get clued in and Oz leads a rescue mission starting with the interrogation of one Riley Finn since Oz could identify his scent among the people that abducted Spike and Veruca.
Do I know any further plot? No. Do I know this fic would end with Spuffy as well as Oz, Willow and Tara in a polycule? Yes.