The stake plunged through Angel's heart. Angel disintegrated in a cloud of dust.
And, as typical for vampires in Buffy's world, all of Angel's clothes and possessions disintegrated too, including the jersey--which was currently his T-shirt. And including the rock, which Angel was carrying.
With the disintegration of the jersey, Jon and Karyn returned home. Jon was in front of his TV set with Karyn, who was lying on the floor. She was pale and didn't look good... he felt for her pulse and there was none. She was dead.
Jon looked around for the rock. It was his one hope to save Karyn, but he eventually realized that Angel had had it--and therefore it was gone.
What could he do?
But in the Buffyverse, now that Jon had gone, Buffy was back to her old self. "What? What?" she said. She only vaguely remembered what had happened... Oh no! There was a magic stone, even though what she recalled was so hazy. Spike had used magic to make her have sex with him! She felt so violated. Sleep with Spike? She'd die first! Yet now she felt so attracted to him. And Spike had made her kill Angel too! It was horrible....
Her friends had left, maybe to make plans. Now she was there with a female Spike, who she couldn't help lust for but couldn't touch either.
A girl tapped Buffy on the shoulder. She turned. "Who are you?" she asked. "You should get away. This isn't a safe place."
The girl whispered so Spike couldn't hear her. "You can call me Anya. I'm here to help you, Buffy. You're a woman who's been wronged by a man, right? You want vengeance, don't you, for what Spike made you do? Wouldn't you want to wish something were different? I can grant you your wish."
Spike, sulking in a corner over being a girl, finally realized there was an intruder around, and thought up a command for Buffy....
"If you can help me, Anya, I'll take any help I can get! Make it so I don't have to obey Spike, give me the magic stone, and let me make Spike pay for what he did... for what she did...."
And that moment of hesitation had doomed Spike.
Anya granted Buffy her wish. The stone reintegrated in Buffy's hands, and the command spell was gone, but she thought it amusing to leave the lust spell behind--which after all Buffy had forgotten to mention. Now, making Spike pay... that was, to a vengeance demon, the pleasurable part. She decided to... No--that wasn't even necessary. She didn't have to do anything except give Buffy a few ideas and let Buffy do the vengeance herself using the stone.
Anya whispered something into Buffy's ears, then walked away. And Buffy held the stone and said "I wish...."